If there are sags in your panel assembly when you pull your cover closed, that means that your short rollers have missed the ramp and are under the rail instead of in the rail. This document will assist you with getting your roller back on the correct side of your ramp so that it will roll up the ramp again.
Back the ramp adjustment bolt (#1) out so that the ramp (#2) can be pushed toward the bed wall to allow the short roller (#3) to move back in front (cab side) of the ramp. Then, adjust the ramp as shown in your installation manual for the Final Ramp Adjustment.