geeeeeez.... that's so bad???? does your LFS
have a return policy or anything?? if the tank has only been setup for a few of months I would say a skimmer may be a good investment, just watch your tank parameters for a few months for nitrate/ammonia. as you add more fish... it's more pollution. so maybe at a point the canister filter might not be enough or it could possibly be perfect. I personally have and overkill running in my tank. eg: refugium, skimmer, biopellet reactor, uv
sterilizer, crushed coral filter and a whole bunch of media and the sump is about as long as my 10ft tank. The size of my sump is a massive overkill but I don't like to take chances.
The safer road would be to buy a decent skimmer and get it working on the tank.
Or just leave your tank as is and test the water regularly until you've got all the fish you want and hopefully the canister filter only setup will do the job.