There's two main culprits for an alt mode that doesn't line or up scrapes the ground:

  1. Ankle joints: get the feet into their spot under the roof of the car then put your thumb on the ankle joints and push them towards the rear of the car. It can be quite tight but obviously make sure both are pushed back as far as they can go.
  2. Waist swivel: he's one of those Transformers where the waist has to be dead centred to line up perfectly in alt mode, and often while fiddling during transformation it can come out of alignment, so just keep an eye on it!