Most states require on driving tests that you turn your head to look backwards when backing up, moving while using your mirrors will mean failing if that is the case in your state. You can check your mirrors, but once hitting the gas you must be looking in the direction your are moving. Check what the rules are in your state before you take the test. Probably part of your test will be simply to back up, not even trying to park, and this would be another case you need to actually turn around. Unless things have changed now that cars have cameras etc. I doubt it though.
Practice parking. Find out how much space they give you, when I took the test they had orange cones I had to park between, and take the actual car you will be taking the test in and practice several times using something to mark the space you will need to fit in. You need to be within a foot of the curb most likely. When I took it, I had to park, actually put the car in park, and that was the signal I was finished.
The trick is to back into the space by cutting hard towards the direction of the space and then straightening out. If you don’t get close enough to the curb the first time, you’ll never make it into the space well, especially if you have a larger car. It does take practice, but once you get the hang of it, it’s pretty easy.