[Bri26]

I would check that all the track pieces have the rails either even with or slightly above the track surface. I have seen some Carrera GO track pieces with the rails slightly below the track surface. If you have any pieces like that, I wouldn't use them.

Secondly, be sure you widen out the end of each braid by pushing the braid end towards the front of the car with it up against the bottom of the chassis. Then angle each braid down so it makes good contact with the rails but not too much that the front wheels don't turn.