Hi there! Thanks a lot for playing and letting me know where you got stuck!
That portion of the game was actually designed with a double jump in mind which I changed to a dash at the last day due to a bug. However, I couldnt get around to tweaking the level design itself to make sure the player can still traverse it.
I THINK you can still get around it by glitching over the spikes by taking damage, then get to that ledge with the mushroom in the 2nd screenshot, then roll down the tunnel and up the left side. That or, before you reach the checkpoint, but after you get the serum, force yourself to die to respawn up where the last checkpoint was.
I also notice you have a heart bug xD it should always be 3 max.
Sorry about that! Will definitely tweak for the post jam version as well as add the boss I was working on!