That's a large transplant. It will take a few weeks to heal. It appears that you may have also experienced some shock loss which is usually temporary. Be sure to follow up with your doctor.
18 Days after Hair Transplant
18 days is too early to see anything close to a final result. If you have any other complications you need to see your doctor but the redness of the scalp may take a few weeks to completely resolve. Individual differences might be seen between people in the process of their healing. Discussing it with your doctor would be the best course of action if you are concerned at this point.
It appears to be healing however the area appears very thin. I wonder if you were over-harvested? Ask your doctor.
3800 FUE leaves a big scar as you are noticing and will take time to heal
3800 FUE leaves a big scar as you are noticing and will take time to heal. If your are losing chunks of tissue and not hair it may be grafts that did not take.
Unfortunately FUE Is advertise by many doctors as being noninvasive with no down time which is not true. It usually ties about two to the weeks for healing process.
Donor area healing process
The photo you show represents a normal healing process. The donor area after an FUE procedure can take up to 3 months to fully heal. I would keep the area moisturized and the crusting should minimize in a few weeks.
The white spot with the falling hairs in very consistent with a telogen hair. This is very normal and you did not loose that graft.