Im trying to learn to play the trumpet and I cant get the C note on the scales I have a 3c mouth peace and a 7c I think but I cant get it with either of the mouth peaces If it make any odds I have a Yamaha 4335g any advice

ive got a 5n horn mouth peice. when i started i thought of a simple peice i could play and i liked playing that started on c (for some reason i liked oh when the saints, it just happened to start on c) i heard the note in my head and i could play it, easily.