Sexual excitement is in the brain, not the measuring tape. If she is interested in sexual intimacy, it is not so she can assess your length. Three inches is not a micropenis, and seven inches when erect is going to be a bit long for most women, as you will possibly bonk her cervix. So go gently, and with enthusiasm!!! and the issue will not be an issue. Only men compare themselves to other men, women don't.
I'm not understanding why you would be embarrassed. You are perfectly fine.