Worn piston rings or stuck piston or neither?

i did a compression check a couple days ago and found a 50 psi in cylinder 3. I added some oil and it shot right up which indicates worn rings BUT 4 days later the compression in that cylinder is still at 190 where it needs to be. i did put seafoam in the car recently and changed the oil (pitch black) and then changed it again (but not oil filter with seafoam in it )after a couple days driving and oil it was pitch black. whats going on???????? please help! now i see some milky white stuff on oil cap and white smoke bellowing out exhaust when i hit pedal.