Use the hyphen, a wiser choice. You may check the dictionary: occasionally common cases become one word.
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mitsuwao23Phyllis: Wow, thirteen!Dwight: Yes!Michael: No. No, no. There was wind.Dwight: I was just jogging.Michael: Dwight, there was wind. I want a do-over.Jim: No, no, no, it's not your turn. All right, thirteen is the new number. Oscar, go ahead.If you make too many mistakes, you’ll have to do it over.That passage, particularly the underline
fivejedjon There was windA headwind is a hazard when timing oneself with a radar gun.
fivejedjonI want a do-over.I want to do it again.
Mister MicawberI want to do it again.Is 'I want a do-over' common in AmE? It sounds strange to me, though I have heard 'I want to do it over' - most Brits I know would use 'again' rather than 'over'.