Looks like a limpet, yeah. Maybe a slipper shell. If you flip it so the fleshy part is down, does it cling and move like a snail? Not sure why it's on its back.
Limpets are basically snails with a flat shell, instead of a spiral. Slipper shells are a similar animal, but have a tiny shelf/outcropping in the shell instead of it being completely flat. Molluscs are pretty cool.