What went wrong after my FUT procedure? (Photo)

It looks like you've had some healing problem.  Did the incision on that sided open up?  It looks like there is still some unhealthy tissue on the upper side of the scar.  Hopefully your surgeon has you putting some topical agent to prevent infection and promote healing.  Once the area has healed completely, you need to wait for the scar to mature (6-12 months) and see if the hair follicles around the incision recover.  Once the scar has matured, options would include surgical revision, placing new grafts into the scar, or scalp micropigmentation.  The best choice would depend on how things look when the scar is mature.  In the meantime, growing you hair long can help cover the area.  Keep in close touch with your surgeon during the healing process.

Great question, be patient, it is just one month after your surgery, the wound healing process takes 10-12 or more months for the final results of your scar. I won't recommend ANY type of treatment at the moment. I will suggest you circular massage of all the scar (5 minutes everyday): use two fingers tips and massage the scar with circular movements, it can hurt at the beginning but it will be better every day. The massage will help you to reduce the redness and swollen and remodel the scar. Also, continue your follow-ups with your hair surgeon. Be patient. Good luck. 

The large scar is either the result of a tension closure with the strip being too wide, or a genetic problem with regard to your collagen. The best treatment for this is scalp micropigmentation (see below)