Could you please share at least your data points, otherwise is very difficult to help you.
The only thing I notice that maybe could affect the fit is your function range. Set the range to be positive, change the minimum from -1 to a positive value even very smaller like 1e-5
Or if your first points are negative you should change your TF1 to
TF1 *fitFunc = new TF1("fitFunc", "[0]*TMath::Log(x–[2]) + [1]", -1, 110);
in order to avoid the argument of the log function to be negative