Before trying to turn it again you should remove the valve cover and loosen the rocker assembly. No sense bending a push rod due to a stuck valve.
Mike B
Tap on the rocker at the valve stem with a rubber/plastic hammer. You will know if there is a stuck valve without going thru the adjustment process. Spray a little penetrating oil thru the spring onto the stem for lube.
Kroil is good stuff but JB80 and PB Blaster work well too. Marvel is a little thick to penetrate as quickly.
