Do you have the same problem playing a G major as a barre chord? I know it sounds slightly different, but if you can play the G major barre, just slide down 2 frets and there's your F major. I often have a very hard time with B major because I have large fingers and it's hard to squeeze 3 of them right next to each other. The way I learned all the major chordes was to develop a nice sounding strum pattern and just strum up the major chords in order. It helped me not only develop the finger patterns, but also helped a lot with the chord changes.