20 inches? Are they serious? That’s a lot for a newbie. It’s no fun learning a new hobby if someone’s making you do it at their pace instead of your own. Make yourself a nice cup of tea and relax, okay? You can do it! Learning to knit is like learning to tie your shoes. It’s a muscle memory thing, so a different part of your brain is learning it (cerebellum vs. the cerebrum). This means that you’ll learn best just by doing it over and over again. But once you learn to knit, it’ll become much more fluid. Don’t worry!
Concerning your dropped stitch, it sounds like you may be casting on too tightly. Try casting on with two needles held together, then pull one out after you’ve casted on your howevermany stitches. That’s one thing that’s helped me a lot, since I tended to cast on too tightly when I started as well. The first row is always a little tricky, too.
Oh, and welcome to the forum! This is by far the friendliest forum I’ve ever been on.