Don't think I can add much here hunni,
@AlteredEgo has done a good job at answering.
Yes you sound like you have an average size peen girth wise,
Does your partner have a good control of her muscles?
Maybe she doesn't or prefers not to tighten down!
Maybe her lady bits are a little bigger than average?
I'm sure you're aware every woman is made differently and altho you can can say a woman's lady bits have an 'average' size some will be bigger and some smaller, some will have more control than others etc.
Personally speaking I'm built bigger than average down there and unfortunately have very little muscle control, in fact my bulbospongiosus, pelvic floor is pretty unresponsive if that helps give you an idea just how different we all are.
You need to start by discussing things properly with your partner so you can understand why your not satisfied with your current situation hunni, it's difficult to help with limited information xx