I've been trying to approach a girl for like a month, and so far I've not managed to approach a single one.
I'm 18 years old, and currently in high school. And I would like to give a little backstory just so you guys know why I have a low self image.

A few years ago, I used to be a huge nerd and I just played World of Warcraft all day. Because of that, I've put myself into the fat, ugly video game loser box. Looking back, I was probably a 4/10; not beautiful, but not super ugly either. However, I did feel like I was super ugly, even though I had a ton of friends.
Now, even though I'm on a diet and actually taking care of my face, I still feel like I'm ugly. In fact, I've looked at the faces of other's, and everybody has minor flaws on their face that only become apparent when you closely observe them.

Now, on to the actual point of this post. The fact that I've seen myself as ugly in the past has really lowered my confident. I also don't know if I should approach girls in school or girls in the mall. If I approach a girl in the mall and I make a mistake, then it's not really a big deal. However, I will see the girl at school everyday, so that will be very embarrassing for both of us. But every time that I've went to the mall I didn't see any girls around my age.
The only progress that I've made in the past month was me talking to some women in the mall who were around 30. Not just some small talk, but a full blown conversation about their dogs, their kids and something about Canada.

So, do you guys know what I should do to make more progress?

Sorry if this post has been a huge spaghetti mess, so here's a TL;DR.

*I have a low self image because I was a fucking loser a few years ago.
*I don't know if I should approach girls at school or at the mall.
*My only conversation was one with some 30 year old women.
*How can I make more progress?