How do I tell if I popped a stitch? What should I do about this?

Closures of abdominoplasties are performed with many layers. This is particularly so in the fleur de lis approach. It is possible that something might have broken. Hopefully these are not the plication stitches that hold the abdominal wall fascia together. If you have a new bulge, talk to your doctor. Repair might be needed. If it's a superficial fascia disruption, it seldom requires attention. Those repair themselves. Best of luck. We plastic surgeons actually want to hear from you.

Depending on how hard you were massaging the area, it would be very difficult for you to pop a properly placed stitch.  This early after surgery it is very difficult to determine whether bulge are just swelling.

I'd recommend contacting your surgeon if you are worried that something may have changed with your muscle repair.  They would need to do a physical examination.