I hope you guys can give me some advice about this.

Basically a friend of mine who I've know for a few years now, has a new girlfriend and I guess brought me up to one of the girls friends and offering a double-date sorta deal. He's now asking me if I'm interested to go.

I'm sorta nervous and not really sure if I should accept it or not, I haven't seen the girl yet and she hasn't seen me, but he assured me that she's cute. The biggest concern I have is that I don't want to come off as a complete beta and end up ruining the night for myself.

First off I find it strange that he seems to have already mentioned me to the girl before speaking with me about it, which kind of sets the precedent as him being the alpha and 'controlling' the situation. I'm a pretty social dude, but he definitely has much more experience with girls than I do and I'm a little worried I won't know how to progress and escalate (ie. keep up with him) with this girl, especially considering we've never met each other. Add to that, I think he may have mentioned something about me being interested in a serious relationship, which is certainly not the case.

I haven't accepted the blind date yet, how do you guys think I should handle this situation?

You have 2 options: 1. Decline, sit on ur ass and miss the chance to miss a potentially cute girl or 2. Accept and show up just to see how things will go and stop worrying about what was said... As you can always deny anything that was previously mentioned about you.