gst payment

I am a small trader. I have limited capital. I buy goods from Ludhiana and sell it in orissa. My parties don't pay on time. I have to sell them goods on credit, they pay very late. I can't force them to pay as I fear to loose customers. But as I give them goods on credit and buy goods from Ludhiana with money. I am left with no money to pay for GST on time. This leads to huge fines and penalty. my profit margin decreases. what to do ? Kindly help!