MP3-25 flexible solar panel providing low current
It is a little confusing since you jump from watts to amps and back and forth, but I believe that you do know the difference between the two.

I suspect that even though you are outside, you are not in the full sunlight that the panel requires.  Broad daylight is not enough, it needs bright blistering sunlight.

Remember that a solar panel will output full voltage at light intensity levels as low as 10% of maximum, while amperage is linear.  So 10% light level = approx 10% max amperage (for a given voltage)

You are correct, the short circuit amperage reading should be close to the actual current output.

Also, the smaller panels may not have bypass diodes and so even the smallest little speck of shade on one part of one solar cell will dramatically decrease amperage (I.e, your thumb provides a small amount of shade on the panel while doing the measurement and the amps will drop by 50% or more!)

If you want to map your own I-V curve, you just hook up a number of different resistors one at a time in series from the positive to the negative of the panel and measure the voltage drop across the resistor and using ohm's law calculate the current.

Good luck.