Have you taken your original caliper off yet and cleaned it well and inspected the piston for pits and rust around the pads. The new rubber gasket for the piston bore is cheap and all the old accumulated crud in the gasket groove must be cleaned out. Not a lot of moving parts there to go bad.Should be fine all cleaned up.
If the return hole for the master cylinder is plugged or not working correctly that can cause the front brake to seize or release very slowly. It may need attention also like a rebuild kit or a disassemble and cleaning. A bad brake line that is collapsing can let fluid through one way and not let it return which can cause a seize also. A way to check is if it is seized because of these issues is to open the bleeder and see if it releases quickly.
Lots of things to check down the line if your having a braking problem.