Nah itll be fine, if you can really notice 3 cm that would be pretty crazy
Erase it from your mind so you stop thinking about it. It wont matter.
Turning properly matters the most, get your body perpendicular to the slope and initiate your turns with your front foot. Arms out, you turn where your front arm points.
Don't be scared, the more you lean back and hesitate the worse it's going to be