my girlfriend and I are both snakes and my birthday is 8/11 and she is 7/2 (month and date).

You don't have to worry about it. You and your girl are compatible. It is predicted that both of you have a lot of commons and the same living values, which would make you stick together to fight for it.
Even though there is a problem, you can solve it eventually. Just dispell your doubt and live a happy life with your girl.