6 months after hair transplant. I had 2400 grafts to build my hairline with FUT. Will the density and gaps improve? (Photo)

You need to give yourself more time. usually, my patients have 80% of
hair at 4 months, I am using a very "nutritious" and caring regimen
after surgery. Under usual conditions, you mill see more than 50% of results at 6
months, fuller at 8 and full results at 12 months.
So, give it time! PRP will NOT help anymore, there is no proof that it will. What worries me is the that your hairline seems too low...

It is too early at six months to draw conclusions on your final results.  Give it at least 8 months, and even up to a year, then go back to see your surgeon, review photos and discuss results

At 6 months, there is a suggestion that the grafts may not have fully taken.  Wait another 2 months before going back to see your surgeon