I'm glad you're feeling a bit better about everything Robyn! I've JUST hit my 20w mark and I'm already freaking out!!

It's been so long since I've had a baby in the house, and having thought we were done.. goodness. It's just all sorts of emotional craziness going on in my head!
I can't recall my kids being in newborn/size 1 diapers very long either but I had some big babies. I don't think either of them finished a whole pack of newborn diapers even lol
And like Gen said, as long as you have somewhere for your little one to sleep and a few of the necessities, everything will be fine! And yes, of course, the stores will be open and you will be able to get anything you need as you need it!
Big hugs!! How exciting to be in the last month!!!!