You might get lost the first couple days, but teachers are usually super nice and understanding of it! Schools usually have maps to help you fid your way, and teachers are more than happy to help you get to class! After that first week though, you'll know they layout of the school like the back of your hand!! :D
Also, the first two years of high school are pretty easy. Just make sure you KEEP UP WITH YOUR WORK!! However, Junior year is infamously known as the hardest year, and I can support that claim. The homework is KILLING me right now! But I am in all college classes, so it may be different for others. And just like MCNerd said- it depends on your strengths and weaknesses!
Hope this helped, and I'm sure you'll have so much fun in high school!
Best of luck!! :D