retreat, rebuild

I'm so sad. Had a supply going on for days, and I gave W a 9oz BM bottle, and I went to start the laundry... Only returning to both of my girls in hysterics, and 2oz left in the bottle... Yup. 7oz spilled. Don't know how because when I gave it to her, the lid was tight (just like always). Changed them (C was asleep when W did it), put them in the other crib. 
Just so sad. I work so hard to pump, and I've done it for over 10 months, and this. Yes, it's one time and an accident learned, but that's almost an entire session. :(. Plus, I'm trying to wean them and myself, and this doesn't help my situation. Now, I'm set back, having to retreat back to every three hours to rebuild. Meanwhile, it'll be formula if needed, which I try to steer away from whenever possible. 
I feel worse when it happens to me because I should know better...
Am I the only one who feels like this?!