tldr; at the bottom

Some background:

I'm a 23 year old guy, studying in the 5th year of Med school, that has never had any intimate contact with a girl before. I also stutter (King's speech style), am skinny-fat, I'm pretty isolated even though I crave social interaction (weird, right?). For some odd reason, people past a certain age (say, 40), are always surprised when they find out I'm single. Apparently being tall should make me a pussy magnet.

What made me write this post:

I've been attending a german course for the past few months, where I met this girl. We got along pretty well, joking, talking casually and stuff. I considered her way above my league, since she is tall, thin, a great dancer and also former prom queen. She is involved in a lot of activies within her college and in general a very active person- completely my opposite. On the last day of the course, something inside of me snapped and I casually asked her out. I had dates before, but it was always planned by someone else, and of course there were no second dates. The days before the date, I read a ton of posts on various subs, like r/dating_advice or r/seduction. We went to a pub, talked a bit, saw a movie, went to another pub, talked some more. I drove her back home, she said she had a good time and called it a night. A week later I messaged her with some trivial questions, and she asked me out the next evening(!?). Again, I did my research, hoping for perhaps a kiss. My priority was to maintain eye contact, smile and use the triangle method I read on an r/askreddit thread.

I thought the date didn't go well, so I drove her back in a grumpy mood. Just before she got out of the car, she looked at me and I realized that was my time. I asked if I could kiss her, and she quickly nodded. It's almost as if all the tension from that evening snapped. We suddenly become very relaxed and talked about how we met, what we both felt etc. It was my first kiss ever, and I was so nervous I could barely sleep that night. We went to lunch together a few days later, 2 hours before she had to attend some meeting. We finished early, and as she drove me back home I jokingly asked if she wanted to come upstairs. Shockingly, she accepted, and I had no idea what to do. I made the huge mistake of telling her this: 'I didn't think you would accept my invitation'. We kissed a bit, cuddled, and that was it. The whole interaction was pretty awkward. From that point on, she became distant, totally different from our second date. Almost a week later, I asked her out to figure out what was going on, and she gave me a really long text. She said she has a really rough year at college (6th year, mind you), that I was a special person and didn't want to lose my friendship but our relationship wouldn't work. I texted back that breaking up would be beneficial for both of us, and wished her good luck with school. I was really glad with how things turned out, since at first I was convinced I wouldn't even get a second date! Not to mention I kissed a former prom queen twice! However, I still don't really understand what qualities could such a hot woman see in me.

Present moment:

Anyway, since then, my motivation went through the roof. Some improvements I've made in the past few weeks:

1) I try to look people in the eyes everywhere I go: at school, on the bus, on the streets etc. It's a bit weird, but I'm slowly getting the hang of it;

2) I'm talking to as many people as possible, even strangers; it feels really great to get positive reactions from a person I've never ever met before;

3) I'm talking to a therapist regarding my speech problem, and it's slowly getting better; apparently my stutter is not a disease, but a symptom of a deeper problem;

4) I'm taking a dance class; I've always been the guy that would rather sit and drink instead of dancing, which is pretty pathetic;

5) this is pretty embarassing, but I bought a spray that stopped sweating in the arm pits; I've been dealing with this for a long time, and finally decided to take action; I feel way more confident now, knowing that big pit stains are a thing of the past.

6) I applied and got a scholarship for 3 weeks in Germany as a volunteer; it's not just to experience the medical field in another country, but also because there's a pretty big group of people going there, and nowadays for some odd reason I crave social interaction;

7) I started reading Dale Carnegie's How to win friends and influence people; after I finish this book, I plan on reading Models.

What keeps me awake at night:

The bad part is that I realise all the opportunities I missed thoroughout these almost 5 years. I avoided my colleagues in order to play video games, I declined lots of invitations and, as a result, I have very few friends and a boring life. I know that many students of my age are in relationships, go camping, hiking and other activies together. Me? I go to class, gym every other days, tennis practice once a week and perhaps go out with some friends that have the same problems as me.

I have basically one year and 2 months before I finish med school, and I'm really worried I missed what could have been the best period of my life. Has anyone been in a similar situation? Is there any way I can salvage this situation?

TLDR; 23 year old virgin got rejected 2 weeks ago; I got a lot of experience from the whole deal and am super motivated to make a better life for myself but also worried it might be too late;