I was forced to sign an undertaking and a cheque. now threatening me

I took 20 lakh in a period of 1 year from my friend whom i knew for 8 years.i shared the profit from stocks with him& paid the profit regularly for the past one year but since 2 months i was not getting any profit.so i told him that i will pay 20 lakhs in some time but he forced me to sign a 100 rs stamp and cheque of 50 lakh.now he is threatening me that unless i pay him 50 lakh he will drag me in court.in stamp i wrote that i took 50 lakh for business and i shall pay 5% interest per month.i do not have any property or job or business in my name at present.cheque is dishonoured i stoped paymn