That's fine -- a crew member directed you up front. You weren't trying to get there on your own. The forward lavatory is reserved for F customers. Part of the benefit in F is the use of a lavatory that has less traffic. It is a serious degradation in flight quality when coach passengers come into F. I find most FAs reasonably good about policing this but there is room for improvement.

Back to my initial question -- why did the OP feel the need to go to F? What is wrong with getting supplies from the rear galley where OP belonged.