Once you turn the drivers side camshaft that additional 90 degrees to the timing mark the camshaft will stay there, However it doesn't take much force for it to spring back. Like I sad before it sounds like your camshaft pulleys are in the correct position but the only thing that is questionable is what mark do you use on the crankshaft? Luckly you have two things going for you: 1. Its a non-interference engine, so you wont bend valves if you crank the engine over. 2. You have a 50% chance of getting it done right if you just flip a coin and pick a mark to line your belt on.
Pick a mark to put your belt on and take 20 minutes to take the valve cover off. confirm that the dots on the idler gear and cam gear are aligned. Slowly turn the engine while you look down the spark plug hole and confirm that the valves are moving accordingly for all 4 strokes: http://www.youtube.com/watch?v=OGj8OneMjek
It should be pretty obvious if something isnt looking right ie. if the intake valve is open and the piston is moving up then you know to use the other mark on the crankshaft pulley. Once you confirm youre on the right mark button the engine up fill with coolant and turn it over!