I got hired at bestbuy I had to take my drugtest today I'm sure i'll pass but I was arrested earlier this summer for possession of cannabis, I already went to court I wasn't convicted, my case is still open but I took the 8hr course/class this past week and should be closing soon, would that prevent them from actually going through with the hiring process?

I think it wouldn't prevent them from hiring You, but they would simply take someone else.
However, good luck with it.

Where you asked if you were ever arrested or just convicted? Did you tell them about the arrest on your app and were you still hired?

As long as you've honestly answered all their questions and you pass the drug test, I don't think it should affect your chances.