Seriously — it’s so easy to think you know a song perfectly, but then suddenly you have to play it with headphones on and an annoying click in your ear and the whole thing falls apart. When you’re practicing, try to replicate the environment you’ll encounter at your recording studio as much as possible. It’ll help worlds when you actually get in there.
While the major scale is ubiquitous in contemporary western music, don’t let yourself feel too much pressure to master it right away. It’s a complex and nuanced scale like the rest of the white-key scales, and it will become more intuitive the more the time you spend composing with it.