Even though she says so, that she is ok with it, is my Grandma 100% ok with me as a Gay Teen?

I think she just didn't think about it, if she is so cool and accepting then why would you think she would all of a sudden become so judgmental...? You are still young maybe she just felt awkward getting something for the guy who might be just your first love, put yourself in her position. Is your bf close with your grandma? But I hope all works out with him and your grandma...