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An average human masses 60Kg. The largest bird ever to fly, Argentavis, massed about that much.

https://en.wikipedia.org/wiki/Argentavis

So it seems reasonable that flying creatures the same weight as a human need to be reasonably close to Argentavis's size. Argentavis' wingspan was about 6m, and wing area over 8 square meters.

Assuming that your scapulae-wings are somehow as light and strong as stretched skin and feathers over an articulated bone frame, one would expect each scapulae-wing to be almost 3m long and average 1m wide, while not contributing much extra mass to the person at all.