Did you look on the bolt to see if you are to use cool, cold, warm or what to wash It? some of the muslins today are stating cold water, delicate cycle, low heat for drying. I always use at least a half cup of white vinegar put in the softener dispenser and let it go. Some of the inexpensive muslins come out quite nicely. Muslin in general is not what it used to be, just like some of the fabrics today. Then I starch it and it is ready to use.
Good Luck
Suzy