Again... "swords - not words!"
It does not matter if you "call" yourself boyfriend / girlfriend or not, as the reality of your feelings, acts, and shared intimacies will certainly be primary. If you and her are b/g because you asked her to be you g-friend, and the other guy comes along and she (for instance) kisses him - does it matter what you called yourself?
But, if you insist, I think the appropriate line is "Will you go with me?"