Missed 3 days of doses

Hi, I ran out of Lexapro (10mg a day), been on it for 3 years. I’ve always been good about taking it and never skipping doses, but due to my fucked up work schedule, couldn’t pick up my refill for the past 3 days. (I’m going now to get it, hubby is driving me because I do not feel well at all). I thought I’d be ok for 3 days because I’ve had a steady blood level of the drug. Guess I was wrong! Should I take 20mg today, or just take my usual dose of 10mg? Lesson learned-pick up your refill asap! Thanks!