Is vaginal opening won't come back to it's latest original size after having sex with a bigger penis for two days?

Joking right?

It depends on your age, health and ability to recuperate. Having a baby is the biggest stretch. Coming back from that may take weeks. Do your kegel exercizes.

I'm sure it probably loosened you up some. But probably not that much. If you want to stay tight, do like simoneaugie says anddo the kegels. They do work ;)