I’ll bet that your OG readings are off because the wort isn’t well mixed in the carboy. Did you do a partial boil, and add a gallon or two of water into the carboy to get it to 5 gallons? It is very hard to get it mixed up, there isn’t much headspace in 5g carboys.
I gave up trying to get OG readings, because (a) the readings were always wayyyy off, (b) when I started I never had a good way to get a sample out of a carboy and the chance of infection etc, and (c) with an OG reading there wasn’t anything I would or could do to change it at that point, nothing actionable from knowing the number.
If you’re doing extract, it’s been mentioned on these forums a couple of times that with extract all you are doing it adding the water back in so it is very hard to miss the OG. The yeast will agitate the mix during fermentation so there isn’t much to worry about.
This is where RDWHAHB really helps out. No matter what happens == you’ll have BEER.
BTW I just looked at my notes and my FG was 1.010, not temp corrected, I used the liquid yeast, and my hydrometer isn’t calibrated. There have also been mentions that this one takes a while to ferment out, primary fermentation is slow and steady. Mine also needed some time in the bottles (more than a month) to condition so the flavors could smooth out.