I'm not good at sex and my penis is small says my partner

My partner and I have been having sex for two times now , we do one sex per month and we just started having sex this may.
I was teasing her, that her pussy is so wet when we have sex and smells like onions -_-(we do sex when shes at near end of her period so she will not be pregnant)

Then she tease me back saying my penis is small and I don't know how to have sex.

Well that's the truth and it saddened me because I only got 4 inch penis and it's been 3 years since I have sex :(
I have been doing exercise to increase my penis size and thinking of buying some penis enlarger or enhancer.

Any guys feel their penis is small and is conscious too that can give advice on increasing its length and grit.