I liked the puzzle to get the petrol but sometimes had difficulty knowing if I was missing something or if I was just having difficulty with the controls. In the past I've had difficulty with jumps clinging to walls in unity, and the solution I found was to check if the user is telling the character to go towards the object they're colliding with and if so override the velocity to only the components parallel to the surface (perpendicular to the direction of contact). Hope this helps