I read in another post that the plastic sleeve is a tight fit on the stantion. My old aluminum one fits like the proverbial cock in a sock. It's not tight ( maybe the misses' sock) .but a good sliding fit.
The damper sleeve should be a loose sliding fit on the stanchion and neat/tight fit in the slider.
The plastic sleeves were probably lighter and cheaper than turned aluminium,and worked the same.Put the thick end toward the bottom.
I can only suggest draining the oil and re-filling with the correct amount of oil.Then take a level measurement with the forks extended,for future reference.