I'd really like to be able to give my girlfriend everything.
That's nice of you. Why do you want to give her everything?
She is always so good to me and I want to return the favor.
It's good you want to provide and be there for your partner. It shows that you are in a healthy relationship together and value each other.
I know, that's why I wish I could do more.
I'm sure she appreciates all that you do for her, so you shouldn't worry about being perfect.