Sensing weight with strain gauge, InAmp, ADC & Pi
You need to use the sensor in one-half of a wheatstone bridge circuit. The other half can be made from two reasonably identical resistors forming a potential divider like the strain gauge does.

+Input of instrumentation amp to centre point on resistors and -Input to centre-point of gauges: -



The two 350 ohm resistors that feed the lower input are the two reasonably identical resistors. Your strain gauge is the two resistors to the left feeding the upper input. In fact the inputs can be reversed. Ensure your power rails are sufficient for the AD620 - remember the common mode range that this amp needs is: -

(-Vs + 1.9V) to (+Vs - 1.2V) so if you operating it from a 5V rail and ground it should be OK because the mid-points of the voltage dividers are at ~2.5V give or take a few tens of milli volts.

Black = lower end of the two left resistors, white = upper end and red goes to the IA input. You'll also need to connect the reference input to (possibly) half rail and note that it is usually reasonable to use the junction of the two reasonably matched resistors and maybe add a 10uF cap to ground but check the IA data sheet on this.