I'm not motivated to comment other suggestions, just a few remarks. I understand, that this is a simulation only, not a real circuit. In a real circuit, I would fear overload of Q1 that isn't able to withstand 1,6 W dissipated power it must handle at maximum with the values given in the schematic. This would not happen in normal operation, but with the output transistor near saturation.
I also understand, that the discussed problem (output voltage too low) is observed with the values given in the schematic, not with different load or input voltage. In this case, I wonder, if V1 may have a hidden inner resistance, that exist as an option with MultSim.
If the observations have been made with a real circuit or with different part dimensioning, I would like to see the real conditions. For an analysis, the node voltages in limited operation point would be interesting.
The circuit also may have stability issues, that would reveal in a transient analysis or in a real circuit.