To be honest, I don't think it will have a big impact, so just choose the option that's easiest for you.
I skipped my Epi dose the day before because I was exhausted from a hectic day and overlooked the evening injection. Following a 20-day course at 0.5 mg, that missed one was on day 15. Should I double up this evening or stick to the normal amount and stretch the whole thing to 21 days instead? Which approach is preferable?