Whats going on with my relationship?

Theres this girl ive been having a thing with for about a month now. We hang out all the time and such. Ive made out wither her twice and kissed her aswell. The only thing is ive never asked her out. She was all bitchy to me at school today while just yesterday she was so sweet. Will girls loose intrest if you dont ask them out officially? What should i do i really like this girl!!