[gumpzilla]

The first few responses in this thread seem to be suggesting that it's her problem. I think it can easily be your problem as well. If you're nervous, you might have trouble being fully erect, and then it's going to be surprisingly difficult to accomplish anything.

It's going to take several tries before you get good at it. Be patient, and try a bunch of different things. Whatever you do, do not try and assign blame or suggest that any difficulty that you're having is somehow related to her anatomy.