1) it is necessary to peruse agreement signed by you to advice
2) record his threats and file police complaint of criminal intimidation under section 506 of IPC against him
3) you cannot be forced to purchase his land for Rs 35 lakhs when loan taken was for Rs 26 lakhs only
4) express your inability in writing to purchase land for Rs 35 lakhs and seek time to pay Rs 26 lakhs
5) let him file suit to recover the money