At first I wanted to ask if you updated the game because I don't remember many of these blocks.
Then I realised it's because your game is tied to 16:9, while Mac's have 16:10 (less wide) so around one block from each side is off-screen.
> you do keep any damage you take between levels
It might be the case I experienced immediate death. Note though, it's not the expected behaviour. With saves on every screen it makes no sense to have less health on the first attempt. I would say, as a general rule, every checkpoint should restore you the full health (if you are reborn with full health)