2 weeks post-op lipo on my lower abdomen. Is this swelling or is my fat back? (photos)

It's just swelling.  Continue to wear your compression garment and follow your post-surgical care as directed by your plastic surgeon. You can make an accurate judgement with regards to your results at approximately 6 months post surgery.

You are experiencing some post op swelling. I recommend and have my clients go for lymphatic massage as that will help with healing, drainage, pain and a better result over time. Talk with your MD and get set up for at least 3 lymphatic drainage massages ASAP. They will help. Hope this is helpful. JB

Its unlikely that the fat has return.
Its most likely tissue swelling.  There seems to be a crease - most likely from sitting or wearing something tight like a belt or tights.
Are you wearing a foam support under the compression vest for posture?