I think having fantasies about both genders does not make you bi, but this is not the point. The point is that even if you are there is no problem at all. Personally, I do not like labels as they tend to stick even if you change as a person. I never had real crushes as a teenager and I got into a super long term relationship at 17 that lasted for 6 years. I questioned my sexuality after high school for a month as I felt asexual but after getting into a relationship I though I was straight. However, three months after my breakup I started dating women and I am until now. So I would say the only worry is coming out, but until you are sure and have acted on your fantasies you shouldn;t worry