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When doing a spore print for identification purposes you need to do it on white paper. Try verifying the spore print color and see if it isn't more of a pinkish than a rusty color. The pinkish spored mushrooms spore print colors are often tough to tell from various shades of brown, especially if you haven't seen them before.
Your description sounds like a Volvariella. That genus has only 2 species in North America that can get as large as you've described, and one of those is very rare and you almost certainly haven't found it. Which leaves Volvariella bombycina as the most likely mushroom you've found.
There are actually several species of Cortinarius that have a volva, but their volvas look more like ridges at the top of a basal bulb (i.e., like the volva of Amanita pantherina) than the volva typical of Amanita phalloides.