Said something without thinking to my girlfriend and now she's mad?

It was just a careless moment. I understand what you mean, but I think your game plan is good. You seem like a good guy, it's only been a day so I wouldn't worry about it too much. Hopefully you guys can work it out tomorrow! It would be ridiculous if she stayed mad at you much longer because of some comment that was just taken the wrong way. Hope all goes well! Good luck :)