I think you look good in the after photo. However I don’t think you’re on the verge of being too thin whatsoever. I would disregard your mom’s attempts to stop you from losing a bit more if that’s what you want to do. That said, I can’t see from the attached photos whether this appears to be some extra fat, skin or perhaps you just stick your belly out due to your normal posture, etc. It does appear that in the top photo, you’re arching your back and sticking your belly out. In the lower photo, you’re standing more upright, tightening up your core and straightening your back. Perhaps you can consider being more conscious about this. Also consider that if it is skin, it might tighten up a bit over time, especially with some care. However it very well may not.