Actually first I warmed it up in warm water for a few mins, then I lightly stretched it. It would still roll off of the groove but not as much as when I started. Then I got petroleum jelly and I coated everything in that and put it into the groove and it stayed. I assembled it while watching from the side of the mating surface to make sure the O-ring didn't roll up as I was closing the gap. And once it touched I didn't lift the tube off at all. I tightened the bolts down immediately.
