Mine did this for a while untill i took the wheel out, pushed the pistons back into the caliper. put the wheel back in and pumped the lever untill back to normal. one pad was still hitting the disc slightly before the other. so you need to pump the brake lever, and push the disc onto the pad that is catching.
This will move the other pad further out... and the one that is catching back in.
This will centralise the pads.
It's trial and error really.
If you've understood that you've done well. haha.