1) BREATHE
2) It's submitted, move on. Maybe it will do well, maybe it won't... don't stress as it won't change anything.
3) I sympathize with your procrastination problem. I have one too.

If something is really important, remove the temptations. So, if I really want to finish editing a chapter or something, the internet doesn't get connected.
4) Give yourself a reasonable time frame to work in. 3 days would not be enough for me to hammer out a short story and edit and format it. I know I procrastinate and piddle around, but if i set small deadlines in between (like rough draft done by X and edits done by Y, etc) it keeps things trucking along. I still may submit (writing or homework....same philosophy) at the eleventh hour, but usually I feel at least okay about what's going out there.
Editors get a gazillion submissions. They aren't going to remember yours and think "OMG HE SUCKS! Never take anything from HIM again."
On the flip side, if it does well, be happy and acknowledge that you always have room for improvement.