Brew calculator question

I have a pumpkin ale in my primary and before i brewed it I used the brewers friend calculator to figure out an OG and FG. I took refractometer readings after mashing and it read 1.065 and after the boil it read 1.052. On the calculator it had the OG at 1.070.

It's been in the primary for about a week and is reading 1.020 which is .001 different then the calculator.

Why was there such a big difference with my OG on brew day? My efficiency was lower then 75%. Shouldn't that lower my FG too?

In looking at you're numbers, in conjunction with the calculator prediction, it looks to me that your post boil reading was incorrect. If your doing full boils where your not topping off with water your post boil gravity should be higher than preboil as you're boiling off water and thus"concentrating" the solution. You're preboil gravity reading needs to be sampled from a blended wort. If you're sampling from the preboil wort that hasn't been sufficiently mixed together you could have sampled from part of the wort that was more of the first runnings, which generally have a higher gravity than the second runnings. If the preboil wort was well blended well it would lead me to believe it was an issue with the refractometer either not being calibrated or the temperature of the wort not being figured into the equation. You're starting gravity may have been higher going into the fermenter than what you think it was. If you had a healthy yeast starter and a healthy fermentation you probably reached close to the attenuation rate of whatever yeast you used. That attenuation number could give you a very very rough idea of what the OG was as well. Calculators online are not always right, especially given the fluctuations in efficiency that alot of homebrewers have in our equipment, but to have a lower gravity by that much post boil leads me to believe it is something with your post boil reading.

After retracing my steps I don't think I calculated for the temp difference from the 68 degree C baseline. I have a refractometer and I have had no calibration errors with it before.