Low OG - yes i read the FAQ - due to filtering wort/whirlfloc??

Hi i've made my 2nd LME kit and they say the OG should be 1.066. I know from my first kit that the OG can be off d/t mixing, reading from top/bottom of the bucket, etc, etc, etc. The first beer i had was way over and now this one is way under at 1.052?! I made sure to mix the hell out of it by pouring back/forth numerous times and took my readings from the top but its showing 1.052. There is a TON of gunk in the bottom of the hydrometer testing tube but i assume this is due to using a whirlfloc tab.

Could filtering the wort (while pouring into the bucket), using the whirlfloc tab, and/or using a wort chiller this time (cooled from 212 to 78 in about 14 min) make the difference as to why i have such a low reading?

Is this a bad thing?

...or should i just chaulk it up to "OG reading error"

If you steep at a proper temperature, add the proper amounts of extract, and end up with the proper volume in the fermenter, there is really no way to be off by more than ~5 gravity points (i.e. +/-0.005 to your SG) in an extract & steeping grains recipe. It's also nearly impossible to fully mix the wort from a partial boil before fermentation, so the low reading is probably due to taking the sample from the top.