Psh, I'm as skinny as they come and I've never had too much trouble getting the girls I like. So long as you can be yourself and have fun with them, be happy and confident, then you should be okay. Charisma and a good heart are far more attractive things than a bulky body.

PS. 5'8" and 120lbs. I've had seven girlfriends in the past six years. *shrugs*