How to get bigger?

My lady told me that my penis is smaller than she would prefer. I’m 6.5-7inches(I don’t know up to where you measure). And it was a pretty hard blow to my manhood and self-esteem because she’s my first girlfriend and she is my entire world. Does anyone have any tips for how to get bigger if it’s possible? I’d rather not have surgery don’t because that’s pretty invasive.