Sounds like your problem is two fold; incorrect sizing and poor loop installation. It may be that correcting the heat loop temperature is all that's needed to get things under control, but we all agree that you will need a proper heat load calculation, and then a determination of the effectiveness of your loop system. Sadly, at this point,both require an experienced and honest contractor. It is another sad story of un unqualified contractor in over his/her head. Good luck!