First of all, to calcultate the ESL you have not to consider the capacitance under the DC bias, but the nominal value, since the Z graph is referred to that condition.
Then you have to remember that during the calculation we loose the information about the signs since we are applying square and square root operators. In particular we have:
Z^2 = ESR^2 + [wL-1/(wC)]^2
that is [wL-1/(wC)]^2 = Z^2-ESR^2
You did wL-1/(wC)= sqrt(Z^2-ESR^2) thus L =[sqrt(Z^2-ESR^2) +1/(wC)]/w this is not correct
Since we know Z is negative (same sign of 1/(wC)) and ESR is less than Z it must be:
-wL+1/(wC)= sqrt(Z^2-ESR^2)
we can now calculate L as:
L =[-sqrt(Z^2-ESR^2) +1/(wC)]/w
numerically:
L = [-55+57]/(2*pi*2.8MHz)=113 nH