my finger nail got scrapped off. Will it grow back?!

It should. Because the only time when a finger nail can't grow back is when the thing (forgot what its called) that produces the marrow that makes the nail is damaged. And thats just above the second joint in your finger thats closest to the tip. If it didn't go that far you should be fine.

Happened to me a couple of times...

Ya it will grow back. I remember mine fell when I was 8 I think. I had some kind of infection in it and then when I had a bath. Without realizing. It fell off completely and there was not trace on my middle finger of a nail however over time it grew back perfectly:)

As long as the nail bed wasn't damaged, yes, it will grow back. It will take a while, though. Keep it clean to prevent infection.

Theres no way to tell for sure just wait and see.