I think there's a bug with my speed because I bought two speed upgrade but I'm still slow
Still as slow as in the beginning or a bit faster but still too slow? if it doesn't change at all, you could try reloading the page. Then the speed level is loaded from local storage again.
If it's just unbearably slow, there might be some weird issue with my movement system :/
Nevertheless, you have the unique challenge to beat the game without moving lol