How to Fix a Side of Lower Ab That's Sticking out After Tummy Tuck?

Thanks for the question.
It is obvious you're upset with your result. There are several issues.
First - if you are less than three months post-op you should give things additional time to settle down. Swelling in the lower part of the abdomen is usually the last to leave. You don't want to have a procedure to fix something that will get better on its own.
If you are more than three to six months out and there are areas of asymmetry (I don't see those from the photos you've posted) it may have to do with incomplete plication of the lower rectus fascia or a ruptured suture.
If the bulge your bothered by is caused by subcutaneous fat some targeted liposuction may improve the situation.
As with the other posters, I agree you should have a serious conversation with your treating plastic surgeon to discuss pre-op goals and how close you've come to achieving them.
You may also want to consider an exam and consultation with another board certified plastic surgeon.
I hope this helps.

Many patients are under the impression that their tummies will be flat after a tummy tuck. This may or may not occur, even in the best of hands.
If there is fat inside the abdomen, it will bulge out, no matter how well the tummy tuck was done. Fat inside the abdomen is not the fault of the doctor.
Also, there is only so much tightening that can be done on the fascia. If it is weak and ripped, it can be tightened, but only so much. The doctor cannot completely tighten all the fascia and reverse all the effects of genetics causing a weak fascia, of pregnancy ripping the fascia circumferentially, of differences from one side to another, etc. A weak fascia or an asymmetric fascia is not the fault of the doctor.
As all of the other doctors have pointed out, patients must be reasonable about their results. They cannot be mad at the doctor about uncorrectable aspects of their own body.
Usually these misunderstandings can be ironed out in the doctor's office with a frank discussion such as the one above.

There are many potential causes for asymmetry in the lower abdomen following tummy tuck that cannot always be predicted nor necessarily prevented.
Prior surgery such as appendenctomy or chlecystecomy or pfannenstiel incisions can cause abdominal wall weakness with resulting muscle laxity and bulging that can produce fullness that is more apprarent on one side following a tummy tuck.