Error in the gain, Amplifier, DAQ system
I have a strain gauge with maximum output of 5mV


The MAX9613 is a poor choice for amplifying a strain gauge (short story is use an instrumentation amplifier) because it will place a resistive load on the output of the strain gauge (a resistor) and dramatically alter its output.

Irrespective of the feedback resistor, the dynamic impedance looking into R1 (which connects to a virtual earth point) is purely R1. This will produce bad results when you are trying to measure a signal that has an output impedance in the same realm as R1 (1 kohm). Additionally, the MAX9613 has an input offset voltage of 100 uV and so this represents an error of +/- 2%.

You will also get mismatch errors because of tolerances of all your resistors. Try setting up a simulation and alter one value by 1% to see what I mean.

Use an instrumentation amplifier is my advice.