Oh boy this turned into a disaster & a big learning for ya ouch.... Just for laughs did a double sided back lighted large sign cost me $800 to do cost me another $800 to redo what a lesson that was lol.
Ok the paint ya used is not normally what is used & today if you are not doing alot of back lighted signs & get stuck with a clear acrylic USE white translucent vinyl or at least white premium vinyl I have used white vinyl mask that has lasted 10 plus years......on the inside, lettering outside.
Forget paint & not rattle can at all.
Cleaning off what ya have..ya must clean 100% & I mean 100% then clean it again get my drift ?
Since at this point I am not sure what will work best to clean I normally start with weaker chemicals like..Mineral Spirits soaking ... how ?.. lay cotton rags is best , newspaper, paper towels etc. will work also on acrylic pour on Mineral Spirits let it soak then rub off
Ok if not working a stronger chemical like xylene then lacquer thinner, acetone, oh test test test because it may soften acrylic...even Easy Off oven cleaner which I know is too strong.
Like I said before if you were painting alot of back lighted sign the paint used is Spraylat or Grip Flex & they have great cleaners that are fast & low cost.
Remember this is the cost of learning since ya did not go to a sign school or learn from a proper sign shop.