Passive Impedance Match Losses
The matching circuit is showing that the signal is maxed out around
  -11.6 dB. The amplifier has a gain of 26 dB. Does this mean that the effective gain will only be 14.4 dB?


If the 32.69 ohms represents the input impedance into your amplifier then yes, the net gain will be only 14.4 dB.

I have to say that I'm a little confused about why you are using this matching circuit - maybe you have a long feed line from your signal source to the amplifier but, if you haven't, you might find a better solution with a pi netwoork of two capacitors and an inductor or two inductors and a capacitor. It's even feasible that a simple two resistor solution might give better than -12 dB.

If I use an online calculator that adopts the following circuit: -



With 6 dB attenuation (best possible) and trying to match 50 ohms to 33 ohms I get: -


shunt in = 2157 ohms
shunt out = 56.6 ohms
series = 30.3 ohms


There is also this one from Analogue devices that matches to a parallel complex load such as an R and a C: -



And if there's any doubt about the ADI tool here are the plots of gain (blue) and input current (green): -



There is an insertion loss of 1.8 dB and the input current at 100 MHz is 20 mA at a phase angle of 0 degrees. This corresponds to an input impedance of 50 ohm given that the input voltage is 1 volt.