Hmm, ok. So does this mean that when there is no
weight on the scale, the number module say 0.3V, and when you put weight
on the scale, the number goes down to 0.1V?
If yes, then I recommend exchanging the two signal wires from the load cell to the instrumentation amp. Hopefully that will drive the output in the positive direction under load.
If no, then I guess I would expect that when there is no weight on the
load cell the number would be small, and when there is weight on the
load cell the number would get bigger, or vice-versa. In any event, if
putting weight on the scale does not change the display of the number
module in a predictable way, then either the load cell or the
instrumentation amp is not working as expected.
If on the other hand the number is predictable but only moves a very small amount, then probably you can adjust for that in software.
Oh wait! I see it now! You are using a 1meg resistor. I didn't see that in the photos before. The gain of the instrumentation amp is inversely proportional to the value of this resistor. Try something much smaller, like 100 ohms or 10 ohms. 10 ohms is recommended on the web page you referenced.