Gypsum

I bought a bag of garden lime from a garden center, and had a worker put it in my trunk, while I paid for that and some other stuff I bought. Left it in my trunk a few days, and when I went to get it out, I discovered that it was gypsum, not lime. I don't know whether the clerk assumed they were the same thing, or the guy who loaded it made an error.
I wanted the lime to put in my garden, as there is moss growing in some areas that haven't been disturbed in a while. (I know, I should get a soil sample done)
I just read that gypsum won't do anything about the acidity of the soil, and may make it more likely to leach out some trace minerals.
Typically, my soil is mostly clay, persistent even with the compost I have been adding. So, if you were me, would you take the gypsum back or use it anyway? And is it considered organic? I know it is mined, but is it treated?

Here in the PNW, moss is everywhere , so all of the big box stores and nurseries carry moss killers by the boatload. I would take it back and substitute it for iron sulfate. Iron is the active ingredient for killing moss. Look for any brand that has the highest concentration of iron (and therefore much cheaper ) as some of the major brand ones have about 1/3 to 1/2 less in their product.

Here is a good article about gypsum and clay soils.

http://www.douggreensgarden.com/gypsum-and-clay-soils.html