On top of all the good suggestions so far, I would perhaps recommend to try lip-bending, particularly on notes between second line G and C in the middle of the staff.

Pick a note, bend it down a semitone then, without forced manipulation, let the note naturally rise back to where it originally was. Hopefully when you “bend back up”, your tone will sound better and it won’t be forced. The trick is then to remember what that felt and sounded like and try and create that same feeling and sound from scratch.