Quick question. im a hurry to get my car on the road!

Anyone know why the %^& i cant push the piston back?? ive even tryed to push it back with a clamp and its tight, i dont wanna force it and break something.

Handbrake is off, but is there some method i need in order to push it back somehow with the handbrake???

Ive never dealt with rear pads before.

Someone please help asap!