Explanation
It was a mistake that I didn't look through the contract before signing it.
یہ ایک غلطی تھی کہ میں نے معاہدے پر دستخط کرنے سے پہلے اسے نہیں دیکھا۔
"Look through" means to carefully examine or review something.
It would have been the appropriate action to avoid mistakes in signing the contract.