On my game i have a simliar problem I think it could be the use of the Update loop. Perhabs.
I couldn't get over the first "spikepit" ... but nice game, super music!
I've updated the game so now you should be able to get further in the game. Turns out it was because I was using Update, and for rigidbodies you should instead use FixedUpdate. You should be able to complete the game now!
