2006 Polaris 800 Sportsman false HOT reading?

My 2006 Polaris 800 Sportsman has been "overheating" lately. I thought it was just leaking anti-freeze so i poured some in, gave it the gas, poured some more in and by the time i was all done i had poured about 18 ounces of anti-freeze in. I thought that did the trick. Im going up north tomorow and im taking my 800, so i ran it again pretty hard today to see if would overheat and it did, in only about 20 minutes. I let it sit for about two minutes and i was able to take the radiator cap off, so is this just a false reading, because i know for a fact that i would not be able to take that cap off with only waiting for 2 minutes.