Banked turns might come later!
Merging blocks will be possible in the next update releasing in April. There will also be more starting points.
About getting stuck, it's possible to get the back part of the car stuck on the guardrails which raises the back wheels from the ground slightly. I think this is what you're describing. Notice that the car only has back wheel drive!
About the leaderboard, do you play the game here on itch.io? Do you get a determinism error when you start the game? In that case you could try switching to another web browser.