Point of view.
Jumping out of point of view is a common writing mistake because it's so easy to do.
I love, love, love writing in first person point of view.
But the trick is to get into a zenlike mode and BE that character.
That means every single teeny tiny little thing in the story is presented ONLY through the eyes of the narrator.
....unless the narrator (i.e., main character) is looking in the mirror....
....she can't see herself.
So that means, you can't write sentences like this:
My face grew red.
My forehead glistened with sweat.
The character can feel her face grow red or her forehead sweating.
But she can't see it.
So you need to write something more along the lines of this:
My cheeks burned.
I wiped the sweat from my forehead and stuffed the tissue back in my pocket.
See what I mean?