I have fat on my cheeks & jaw which make my face look round & chubby even though I'm fit. What can I do to fix this? (Photos)

I appreciate your concern, however your issue is really extra fat of your neck and jowl regions. While physical examination would be helpful, it appears that micro liposuction of your neck and jowls with possible Botox of your cheek regions may be the best option for you. By utilizing small cannulas expert contouring of those areas can be performed. Your larger cheek region is secondary to enlarged muscles of that area and BOTOX is an effective option to shrink those areas. Come see me or another board-certified plastic surgeon in our area for a full evaluation. Good luck.

Hi!
It looks like you have a large master muscle, which is making your jaw look wide and your face have more of a square shape. Do you grind your teeth? That increases the size of these muscles because they are constantly working and growing. Injecting a neuromodulator into them such as Botox or Dysport will relax and weaken the muscles, and over time thin them out. This will cause your face to become more heart-shaped over time and also to look thinner. 
There are other interventions you can do such as Kybella if you desire more contouring under the jawline, but from the looks of it, I think a little Botox will do the trick-plus it will help with dental health!