I'm getting a headache going over this situation

Basically, I asked a chick out for dinner. when we met I saw IOIs (glancing when I wasn't looking, etc), also I was in the right place at the right time and I helped her sort out a problem with her clothes. She actually found my facebook through a mutual friend (I never asked for her contact details) and initiated online contact after our meeting. When I asked her out she was really eager to go out with me (I set the date for today, she said she couldn't but instantly said she could tomorrow). I have no idea what I did to deserve this but I don't want to fuck this up.

I already promised to go out with a friend of mine tomorrow. I guess the options are ditch her for him, ditch him for her, or go for dinner with them both?

The dude is no AMOG, in fact he is a very nice guy and was with me throughout the entire school group the last time I hooked up with my ex. He is also quite entertaining, and likes to comment on my plus points (pseudo-wingmanging?) so bringing them both has its merits, but if I do then I'm probably sidelining myself into a situation I can't escalate in.

Also, I am worried that he is better looking than me (I have self esteem issues I never really ironed over) and this may affect my outcome independence. He certainly is more fit than me, physically.

I would hate to ditch either of them. The dude would probably understand, but I'd hate to do something like this.

I feel like I am assessing too many factors at once. Which ones are the most important? Which ones should I focus on? I don't mind getting laid later, but I don't want to lose the opportunity to get laid simply because my friend is too much more handsome than I am. My head hurts. I'm sorry if I'm blind to the obvious.