OG question

First let me say SORRY if this is a repeat question (I'm sure it probably is), but I couldn't find anything.
I just completed my 2nd Partial Mash batch and both times my OG reading was about .05 away from what the instructions said they should be. Is this a MAJOR issue, and how can I fix that next time. I'm following the instructions as closely as I can, but can't seem to get the OG correct.
When I started brewing ..my buddy that taught me said that all I need to do to get my alcohol % is to take a % reading before the primary and then take it again before bottling, subtract the 2nd reading from the 1st and there is your %. Is that a correct way?
Thanks for all the help that I always get on here ...
Rick

Do you have a recipe?

What was your actual reading and how did you take it? Temps?. What was your Target OG?
If you were shooting for 1.055 and you say you were off by .05. Then you hit 1.005? Or were you only off by .005?
I wouldn't think that is a major issue.

The equation to figure out Alcohol% is
(OG-FG)x131= %

Target was 1.061
My measurement (taken right before adding the yeast at approx 80 deg F)
was 1.051
maybe it's not that far off, I'm just wondering what that would do to the alcohol %. NOT that it matters too much, I'm more into taste then into getting drunk.

Thanks

Won't effect taste much. Your og corrected for a 60* hydrometer is 1.054. Since its partial mash both your mash efficiency and water volumes would play a significant roll in why you undershot a bit

so how would I fix that for next time?
I did my mash at around 160 deg for 1 hour in 1.5 gal (per instructions)
then sparged it with 3 quarts of 160 deg water ..added 1 more quart for a total of 2.5 for the hour long boil.