new Clarks m2 hydraulic disc brakes won't retract when brake lever pressed

I just fitted a new set of Clarks M2 hydraulic disc brakes.

I aligned the calliper to make sure the rotor doesn’t rub the pads when the wheel is spinning.

I then pressed the brake lever, when letting go the pads stay pushed against the rotor.

I took out the pads, pushed in the pistons with a flathead and tried all above again.

Pressed lever again and same result.

Any ideas?

Many thanks.