Your weight should not do what you described if the tires were inflated properly. Rollers do have a smaller contact patch than the ground because of their roundness, but there's 2 contact patches (in the back where most of your weight is) so the total area should be close to the ground contact patch. I would think the likely culprit is an under-inflated tire(s) (some tire gauges are inaccurate), so I would just pump up the tires until they are noticeably hard and don't pinch when you get on the rollers.