If it's the same version as I know (probably not) then the chorus goes as follows:
There's a little girl and her name is Mary Mac
Make no mistake she's the girl I'm goin' to track
Lots of other fellows they get upon her track
But I'm thinkin' that they'd have to get up early
Mary Mac's father's making Mary Mac marry me
My father's making me marry Mary Mac
Gon-a marry Mary for my Mary to take care of me
We'll be feeling merry when I marry Mary Mac.

As usual you can have my copy here Irish@prof
Mick.