It's ok I think that happens to most people at least once. I packed mine with talcum powder and she was fine, though I made sure to barely cut off any on the next session and use lots of kibble because I was really worried about her becoming a pain to trim. As for walking, I'd just give it a go. If she seems to be feeling any pain you can always go home, but my girl was fine once she stopped bleeding.
Been there, cut that quick. I recommend a styptic pencil to stop any bleeding. Works like a charm on me and my dog but I do have separate pencils for human and canine use since a little blood may be left behind on the pencil.
As for walking I would start with a short one and monitor for any discomfort. Check the pups foot after a short walk and if ok then it's probably fine.