I was in a car and waved my hand to signal the car behind me to move back just a bit so that I could reverse.
The dictionary suggests us to use this structure
wave + somebody/something + adverb / Preposition
wave somebody through/on/away etc
"back off" is a verb but "back" and "off" are also adverbs
If I wanted him/his car to move completely away from me, I would say "I waved him/his car away".
However, I didn't actually ask him to move completely away from me, I just wanted him to move away just a bit so that I could revere my car.
Is it correct to say "I waved the car back off"?