Hi Jake - and welcome to SlotRacer
The Jadlam SLS sets are great - nice step up from the basic sets. The SL2 is particularly nice as it has a mixture of standard R2, tight R1 and fast R3 curves - something you never get in basic sets.
This is the 2021 version. Did you get those two cars? Or are they different in your set?
It's good everything worked fine before you launched the ARC app. That's important to check and it does suggest all the Scalextric hardware is working perfectly well.
I have written quite a detailed guide to the ARC Pro app here on SlotRacer:
slotracer.online/arc-pro-guide
Sometimes, getting the app to connect to your device and can be troublesome. I've given some tips and ideas here:
slotracer.online/arc-pro-guide/problems
Don't worry about choosing a track - if you have a 2-car set like the SL2, just choose any 2-car set on the list. That makes things easier by automatically setting up 2-car race.
Calibration is about setting the lowest speed to get a specific car round the track. It is important for the pit stop functions, which you probably won't be using until you add a pit lane to your set. Just move the slider on the screen until the car goes at a slow speed all round the track. Then you don't need to worry about it any more. I've written more about calibration in this section:
slotracer.online/arc-pro-guide/classic
Hopefully that gets the ARC app working with your set and cars. If not, let us know more.