If you have lots of fresh grease in the spindle bearing it will take a lot of pulling to get that spindle back out. I borrowed my wife's help and we both pulled with a long crowbar on the bolt threaded into the end of the axle. It didn't come all at once; it took pulling for at least a couple of minutes for the spindle to slowly come out far enough to get the snap ring on. That grease has to squish around a bit. A quick search noted 2 specific things that may help. First, make sure you have the correct snap ring pliers (photos of those are on this forum). They will open the ring without bending it sideways. If you opened the original snap ring with pliers that bent it, it will be VERY hard to get back on and seated. You'll probably have to buy new rings. Second, make sure you removed the old flange gasket. If you doubled up that gasket, no ring will go back on and seat correctly.