Is it okay to be scared when you're at a preteen age left alone at home?

It's ok to be scared in general)) If you're left home alone for the first time, things can be daunting... Look around first: you know your home, you know that all the unsafe stuff is off. If you don't know how to turn the unsafe thing on, don't. Call a parent you trust.

Think of your home as a nice place. Just because (or actually because - but I'm projecting) your parents left home, it doesn't become a battleground. It's chill, free, calm. You can do whatever you want. It's fun)))

Confide in an imaginary friend/irl friend online/Deity you worship - anyone you can trust. Better together, right?)

And now - be brave)) Do what you usually do and ask your parents for help from time to time. All the best.