When we got the coop, it said it would hold 6-8 chickens... I suppose it was wrong, what should I do? They are still small, so it’s not too crowded, and they always have access to the run during the day....
Unfortunately, commercially-made coops almost always say that they hold more chickens than they really should. They take advantage of beginners who don't know what they should look for.

You've already started to expand your run. In time you should work on expanding your coop too.
If your run is predator-proofed you can leave the pop door open 24/7 and that will help.