And for Ka I just did Ka=[A-][H+]/[HA]

Funny thing about this question is that you don't need to calculate anything.

You started with some unknown amount of acid. Your neutralized it. Then you added exactly the same amount of acid. Thus in your solution there are identical amounts of both acid HA and its conjugate base A

^{-}. That means pKa = pH

Note, that what you did - adding and subtracting H

^{+} concentrations - has not changed anything, as concentration of H

^{+} is sevral orders of magnitude smaller than concentrations of both HA and A

^{-}. Try to calculate ratio [A

^{-}]/[HA] and ([A

^{-}]+H

^{+}])/([HA]-H

^{+}]) and compare these numbers.