Most of my plastic kayaks have had such dents develop at one point or another. You should use saddles like Yakima Mako to carry them and not tighten them much (these saddles have a rubber traction strip that makes it really unnecessary to strap hard to keep the boat in place). Still, in hot weather air just sitting there a long time the boat will dent even if not strapped. Normal. On my kayaks some careful heat gun use and some weight well distributed inside fixed them as new. Some bumps just disappeared on their own in the sun when the kayak is just left on its own. Without access to the inside to push the dent out, you might have more difficult time fixing yours.
For storage, I don't just drop the ski on a skinny wall rack or on the ground - it will dent or change rocker. Use straps to hang it from the ceiling with even weight distribution and rotate it from time to time to change the way it weights itself against the straps. This works for me in a 4-season location out of the sun, might not be good enough in a hotter place...