If your OG was supposed to be 1.080, and you came in at 1.071, then you did NOT hit 80% efficiency. The recipe should have assumed 72-75% efficiency, so with 72-75% efficiency, you would have been at 1.080 OG.
You had an actual efficiency closer to the high 60s, like 66-68%ish. At 80% actual efficiency, you would have been closer to 1.09 OG.
Did you not plug in that you yielded 5.5 gallons instead of 5.0? One of the numbers in your efficiency calculation is off.
Is this a pre-boil efficiency calculation, or post-boil?? Did you account for temp?