Fat Fingered Financial Fiasco

So, my husband and I have separate accounts and this works out pretty well for us. We made my account the primary one and it's the one that most our bills get paid from cause I like to do most every thing online (except for when they charge outrageous "convenience fees" - but that right there is a whole topic unto itself). We have been happily transferring funds back and forth for some time now without incident. Then comes what I have dubbed "the fat fingered financial fiasco." I messed up to the tune of $600. I meant only to transfer $212 to cover a bill and ended up transferring $812. Wow, was I high or something. I really have no excuse and didn't even realize what had happened until Nate (my awesome husband) went into check his balance and found it in the negative. Oh boy...I have made stupid mistakes before and undoubtedly will make many more before I'm through on this earth, but 5 overdraft fees later, I hope my future mistakes are far less costly.