did I mess this up?

Ok I made 2 ciders about a week ago, both were made almost identical,

4 gal apple juice
3 cans conncentrated apple juice
2.74lb pure sugar

Here's where they differ, in one I added enough water to bring it up to 5.5gal in a 6.5gal fermenter, the other I didn't fill it up any furthe because the plan was to add 10lb of frozen blueberries, however my wife went into labor the following day so I couldn't add the berries. Today I just got a chance to check them both out, the one filled up with water was bubbling fine, however the one that was to get the berries isn't bubbling at all, my first thought is because it has to much headspace. Should I just add the berries to raise it up to the correct level or is it already messed up?

The headspace really shouldn't matter. I've fermented in containers that are 2/3 full with no problem. You'll get C02 to fill most of it, if not all of the empty space anyway. I would be more concerned if it wasn't bubbling at all or hasn't bubbled in several days. Check with a hydrometer if your worried to see if its actually fermenting or not. You've added a lot of fermentables as far as I can tell....it should be doing something.....if it is fermenting......add the berries, wait and enjoy!