PicoScope doesn't know that you are using a special probe, attenuator or anything else. You have to tell it what you are using by selecting the appropriate custom probe. Do this by clicking the channel letter and then selecting the appropriate probe from the dropdown.
Eventually you will add probes to your library where you can edit them and add ranges within the probe. For now, you would be selecting the 60A current clamp 20 amp mode and ensure the amp probe switch is in the 20A position. This will then scale in amps.
As always, make sure the scope is grounded to battery negative and any and all channel grounds are at the same place.