Moving to a larger bore is always likely to present problems in adjusting. As has been said it is important that enough air is going through to produce a steady tone. Do you find it hard playing quietly at all, or is it that you're afraid that the note won't sound unless you give it enough power?
I think sometimes, particularly with a larger instrument, players can be so anxious to get a good start, and not end up behind the beat, that it can sound a bit like a mini explosion at the start of a phrase. I would recommend lots of practice - of course - plenty of long notes and legato playing, starting at a dynamic you feel comfortable with, and then gradually getting quieter, but ensuring tone quality stays good and even.
And congratulations on joining the right section of the band :!: :wink: :lol: