Hi, I'm Just 17 now and I need help with this...

When my penis is Erect The foreskin staysn coverin
the gland completly, I need to know what to do to make
the skin want to pull back because my girlfriend wants me
to have sex with her so I need to know

1: Does havin sex make the skin want to pull back?

2: Should I have sex with her?

3: Is this common in males my age?

If you could help me, that would be great!!!!!!! :)
But please hurry cause i don't think she wants to wait