Bulge in lower abdomen 3 weeks post op. I wear my compression garment all day and night. Is this swelling or bad result? (Photo)

Congratulations on having undergone the tummy tuck procedure. What you describe is commonly encountered after this procedure. Patients will like their “flatness” immediately after surgery; then, these same patients are disappointed for a period of time once swelling of the tissues occurs. In the longer term (this may take several months and even up to one year), the swelling dissipates and the skin of the abdominal wall "redrapes"  over the smaller underlying  musculoskeletal framework (where the abdominal wall muscles have been brought together again in the midline).
Sometimes, fluid accumulations (seroma or hematoma)  may cause the appearance of increased swelling; best to have your plastic surgeon evaluate you (again) if you have noticed significant changes and/or have concerns. I hope this, and the attached link, helps. Best wishes for an outcome that you will be very pleased with long-term.

The bulge could be caused by a number of things. These include redundant skin and fat, intra abdominal fat, subcutaneous fluid collections, normal postoperative swelling or lax abdominal wall musculature. Knowledge of the operation as well as an exam is needed to know for sure what the cause is. Allow additional time for healing and discuss your concerns with your surgeon.

At three weeks you are still healing and likely pretty swollen. Be patient with the final results. Good luck.