I will not go into either the mechanics
or the ethics
of your sexual exploits (such as why you would ever
propose to do this without a condom?).
Suffice it to say that we have didactically described the exercises you need to do to loosen your foreskin and
frænulum, and of course in the longer
term, that is your solution.
What I am
going to suggest (and as variants of your question appear so
frequently on purported "help" sites such as Yahoo!Answers where it is a great waste of time replying,) is that your actual
problem, is "stage fright" ("performance anxiety
") whereby surprising as it may seem to you, you can not
get or maintain an erection merely because you wish
to or even because you are squeezing up to a (presumably) naked and receptive young lady.
- fear (of what you anticipate will happen because it did before) together with whatever degree of discomfort you experienced due to this escapade - is a very effective suppression of erectile function. You actually do
have to be "in the mood" for it and have a positive
expectation. As soon as something happens that you sense is "wrong" - not feeling what you expect, or a "twinge" of a tight foreskin being pushed back - you lose your focus
on the sexual excitement, and start worrying about what will happen next. So as soon as your erection fails to meet expectations, your fear is confirmed and becomes conclusively stronger.
I could be wrong, but the same thing would (and probably should
) happen if you hear her father approaching on the other side of the door.