Green’s Dictionary of Slang

about right adv.

to the best extent possible.

[US]Bartlett Dict. Americanisms (2nd edn) 2: To do a thing about right is to do it well.
[UK]Hotten Sl. Dict.
[UK]J. Ware Passing Eng. of the Victorian Era 209/1: Right, About (Peoples’). Modest self-depreciation, or depreciation in general; not absolutely right, but nearly so, e.g., ‘I thrashed him about right’.