Forge case of Cheque Bounce against me

i purchased a running business, deal is finalised in 5 lakhs, i given him 1.5 by DD and two cheques of 1 lakh each from by brother account, out of one is PDC of 15 days because i was sort of money, so i given him PDC as a security cheque that i will give bal in few days and made an agreement on which one cheque number is mentioned. Same evening balance 2.5 i suppose to borrowed from my friend and given him the cash but instead of 2.5 my friend lend me 3.5 and said take your cheque back. So i have given him 3.5 cash and that i have his signed prove in normal notebook paper. That day he returned my one cheque which is mentioned in agreement and other he said he'll return me when he come next time, after that he making excuses that i am busy ill come later. After 15 days, now he forcing me to pay 1 lakh more or he will file the case against me because in agreement the amount mentioned 2.5 lakhs. Please suggest me what to do.