If you have purchased the plots in 10 lakhs with late payment after exchange of proper words for selling and buying as per the Shariah, and you took the plots in your possession, then you became the owner of the plots. Now, if you sell the plots in 13 lakhs or more or less, and pay back ten lakhs to that person at the proposed time or before, it is also lawful. The profit of three lakhs will be lawful for you. If any of these matters was against the Shariah principle, the ruling will differ. If you have some confusion, submit the question again.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband