Starting my first job (out of high school) tomorrow and I'm really nervous

I'm 20 and I've been looking for one for more than a year, this one was the first job I think I can actually handle physically and emotionally. But I'm really scared, I had 3 jobs before in high school that all ended EXTREMELY fast. I really want this to work, and I feel very unprepared despite my best efforts.

It's a toy shop and they seemed pretty desperate, I got the job 2 minutes into the interview. But I'm still not officially in, I have a trial week that I'm worried about, and also about the work after that, if I get in. I don't have any work skills yet. I know the whole point is getting them through work, but what if I get fired before that happens?

Do you have any tips for dealing with these anxieties?