My guess is you are right.

See this link right here.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/drum-brake2.htm
It has a diagram that shows exactly how it works. And if you read the deion, some cars may have an adjuster only actuated by parking brake and therefore does require parking brake actuation to adjust it. If that's your car then yes, you will need to apply the parking brake. But you probably don't need to do that as you're driving in reverse. You will probably need to pull the parking brake a pretty long distance initially.

You might even have to tighten the parking brake cable some more in order to be able to pull the distance. But if your parking brake acted pretty normally before changing the brakes, you shouldn't need to do that. Just pull the parking brake a long way (may need a little more power at first); release it, then do it again a few times.

Hope this works. Worst case is that you have mis-installed the adjuster -- missed a hole or something like that. Then you will need to open everything up again. But you definitely don't need to adjust the star wheel manually to get to the perfect spot. That technique is only used on drum-in-hat parking brakes where the adjustment is not critical for primary braking function, and an automatic adjuster costs "too much".

Good luck!