Not 100% sure about the tandem belt drive, but on the singles they have the chainring (beltring?) with the edge lip on the outside (opposite of your current setup) and the rear cog with the edge lip on the inside (similar to your setup). Until you have the tension set, the belt won't engage the chainring correctly.

In looking at your setup, I'd speculate that your belt is too large. Not sure you have enough movement in your bottom bracket to tighten that properly. I'd check to make sure you can get that tight enough. If your tension can get tight enough, I don't think you'll have any problems with the direction of your chainrings.

My 2-cents.