Sometimes I want to be a girl, but sometimes I think otherwise

Could be genderfluid, since you describe yourself as feeling here and there, especially if this occurs often.

 

That's how I feel (but replace girl with boy), and I identify as genderfluid. Some days I'm a girl and I'm happy with my body; some days I'm a boy and I wish I had a male body; somedays I'm something in between or nothing at all.

If you feel that you have two distinct, separate genders, you might fit better with the label bigender. My understanding is that the main difference is that genderfluid people feel that their gender changes between multiple genders, while bigender people change between (or can experience both at the same time) two distinct genders. This could be male and female, or female and genderqueer, or any other combination, but what's important is that there are only two.