As long as you have passing grades (C), you'll be fine. No need for paranoia albeit its highly understandable for one to feel that way based on rumors, stories etc. 

The border patrol agents at the airport have no idea on what your GPA is. Also, Working by using SS has got no relation with entry. Its all a load of baloney. 

Technically, you're not supposed to work more than 20 hrs/ week during school session even if you have a valid EAD card but plenty of people including myself worked more hours during school. Also, there were times when I worked just showing my SS card and visa (My F-1 visa served as a work permit ) and I wasn't the only one. None of us got stopped, deported or anything. 

Good luck.