if that is the output of the object through json.dumps() printed, then you’re good.
The extra stuff you see in mine is whats there AFTER passing data through json.dumps() (a second pass) Since the string you have is in the columnValues variable - and that then gets put json.dumps as part of data it will pick up the extra \ to escape quotes so the JSON is valid. (and new lines).
Basically, take what you got and put it in the columnValue variable and you should be good.