Newbie! Help with tiny Retro art project

Hi guys

So… I was hoping I could get some help on this silly little project Im doing.
Im an artist and ive made a little retro driving game from a template as a competition.

Ive done what i want apart from the following.
The background still stutters on a long turn.
The cars speed forward if shunted from behind.
I cant seem to get level 2 and 3 to delete without killing level one aswel?!
Id like a fresh leaderboard at the end too without anyone else on so i can see peoples scores for the prize.

Link is above…youll see what i mean.

Sorry about this message that will probably annoy most of you haha but i love retro games and this would be a cool little thing to do on my website. But i still want it to not be janky you know?

Most of you here would probably be able to sort it in 5 mins!

Many thanks
Andy x