Yeah, assuming the stains aren't some abrasive [stuff] stuck to/in the MF material. I *would* try laundering it with some extra attention, and see if you can get the stains out.
Washed car and left in sun and developed some bad water spots. Re washed and some came out. How to remove remaining without buffer
If they're just mineral deposits then vinegar should dissolve them and solve the problem (note it will also remove any wax/etc.). IF they're watespot *etching* you have a different, bigger problem and the car will require abrasive polishing.
I trust you learned your lesson about washing in the sun