This is the pinout of the AD620:

This is a typical usage example:

I downloaded the AD620A SPICE model from here. When I doubleclick the (.cir) file it opens in LTSPice. After placing my cursor on the line starting with '.SUBCKT AD620A' and rightclicking there is an option 'Create Symbol'. The resulting symbol shows different ports so I think I need a different model.

No, that is not it. All four downloadable models have the same pins. I think I need to modify the symbol myself.

This is the result after simulating in LTspice. The simulation is very slow and the line in the graph is somewhat glitchy, but it does show a correct gain of 2.

Here is the gain formula:

And here it is on the breadboard (with an extra current limiting resistor).