Leaves

I'm Working in a company. It has been almost 6 months. And I am also studying at college. But now i cant handle both at same time. So now i want to leave my job but my employer told me to do notice period of 3 months otherwise i have to pay that 3 months salary to the company. And I'm not able to serve 3 months of notice period. Can I take leaves when I'm on notice period? Additionally They took my original 10th Certificate. And I have also Signed on Confirmation letter. Can you please guide me what should i do?