Are you attracted to her or not?
There's a lot more to sexual enjoyment than perceived hotness. You could have god-awful boring sex with a model and then mind-blowing on-every-piece-of-furniture sex with an ugly fat girl. Your friends aren't as impressed, but are you doing it for them?
Also, you might be willing to try out some more advanced sexual techniques than on a girl you're sub-consciously worried about impressing.
Don't do it if she doesn't even turn you on in the least. Why put yourself through that just for a +1?