you are not stupid, and you did not 'create this problem'.
Feed her next time on the full side, massaging the lumps as you go (if you can), and try to drain it. Sometimes they don't. My DS couldn't drain a boob for some time - maybe 2 months or more. I know it's hard to remember which side yo fed off last when you are so tired your brain is mush but I try to feed off the fullest side first, so if she only had one side feed off them alternativley but if she's managing to drain one and have a bit of the second, start with the second one first on the next feed - eg if DS finished on the left (so had had the full right and then finished on the left) then the next feed I feed from the left first. When they were new I found putting a hairband around my wrist on the last side helped me to remember.

As for the comfort feeds - that's exactly what they're for! Your doing wonderfully!