Hey bud, no need to be embarassed about this or asking the question. Many of us have problems from time to time "getting it up" when we need to. This sounds like a case of performance anxiety to me, we want to make sure that things work sooooo well and that everything is perfect. What happens is that we work ourselves up so much that the anxiety then creates the problem. Once that happens, then we're worried that the lil guy won't work and then he doesn't. So, your challenge is to keep trying and stop worrying. You know it works, because it does for you. Therefore the problem here is in your head. Next time try this....forget that you even have a penis. Focus on your girl, lots of foreplay, kissing and such. Its totally OK to use your hands to help the lil guy, or have her work with it a bit. Patience and understanding are key here, it may take more than one attempt at this, but when all is well...things will be great! One more thing, plan ahead and don't masturbate several days before hand...that may help as well.