If this is your (OP) first folding tire, you may be used to stuffing the tube inside the tire and mounting both sides, or at least most of both sides, at once. The folds on this tire make that difficult. Instead, as Frank suggests, get one side of the tire on the rim all the way around. Then put the tube in the tire and start wrestling (or is that rasslin'?) the second side of the tire on. With lots of luck you won't push the first side out while mounting the second side.