Lisa Lynn Sowder, MD (retired) - Account Suspended says:
You have had some necrosis of the skin and fat at the area under the most tension. This will eventually heal in and probably end up looking okay. If not, a scar revision may be in order. It's important to keep this area clean and if I were your surgeon, I would have debrided...
Yes, you have a seroma. You need to see your surgeon. Let's hope they are in the same country/ state/ city as you are.
Seromas are a common but annoying complication of abdominoplasty, provided they do not become infected.
Best wishes, Mark.