Yep, more cake batter. If you are getting too much of a dome, lower your oven temp by a bit. You also may not have to cut off ALL of the dome depending on your filling. If all else fails, just bake more layers. It's more about the height of the finished product than the exact number of layers inside.
When I use 2" pans, I fill approx 2/3rd full and bake at 300 - I get pretty close to 2" layers this way. I recently borrowed some 3" pans and put the same amount of batter (# cups) into them as I do my 2" pans, baked on 300 and had almost 3" tiers.
Thank you everyone! I have been filling my pans 1/2 full, so I will add more batter to them..hopefully it helps. I forgot to mention earlier that I always use bake even strips on all my pans (except 6").
I tried to pull up the tutorial that was suggested. The tutorial itself would not pull up but the responses did. But, I did find another one. I have two cake orders for next weekend that I will be using the collaring technique. I'm really excited. Thank you everyone for all your suggestions. I will report back on how they turned out.