Paying back my maternity leave pay

I am currently on maternity leave and struggling with the idea of going back to work. I work for a very small company and was given 12 weeks of maternity leave at 50% of my pay. Our employee handbook states that you must return to work for 12 weeks or you will need to repay your maternity leave pay. My question is, is this legally allowed? I live in North Carolina for reference. I have every intention of going back to work for a minimum those 12 weeks just to give it a shot, but I'm wondering if That would legally withsand should I go back for four or eight weeks and just simply do not have it in me to stay any longer.