Oh no 
top
Copper grease has metal particles in it, and shouldn't go anywhere near pistons AT ALL.
You need to get that totally off properly with brake cleaner and a good scrub.
It will damage the rubber seals and stop the pistons from sliding, as you're unfortunately finding out the hard way.
Pistons should be smeared with red rubber grease which you can buy in small pots or even sachets, and is kind to rubber seals and will protect the pistons.
I would do that sooner rather than later as well before you cause more problems.
top Copper grease has metal particles in it, and shouldn't go anywhere near pistons AT ALL.
You need to get that totally off properly with brake cleaner and a good scrub.
It will damage the rubber seals and stop the pistons from sliding, as you're unfortunately finding out the hard way.
Pistons should be smeared with red rubber grease which you can buy in small pots or even sachets, and is kind to rubber seals and will protect the pistons.
I would do that sooner rather than later as well before you cause more problems.
More people are born because of alcohol than will ever die from it.