Like some of the other people who've given you great advice I'm also a professional woodworker. The first thing I want to reiterate is what others have said- there comes a point when you have to let your project go. Do your absolute best work always, and once you're done don't sweat it. You'd be surprised how much time even experienced woodworkers spend fixing mistakes. They always happen. Fine Woodworking has even written articles on how to fix mistakes. That said, here are a few tips I'd try and incorporate:

- on hardwood, following planing I don't start sanding with a grit more corse than 100. Fairing is a bit of a different matter, but softwood is really soft, so go easy. 60 grit is brutal, and 80 isn't much better. It's easier to sand a little longer with a finer grit. There's a lot less chance of making a mess.

- remember that sandpaper is a cutting tool, just like a chisel or a plane. Don't be shy about ditching your sandpaper the second it seems like it's not cutting as well as when you started. If you don't, when you work with softwood it can cause a lot of problems. It won't cut the harder annual rings as well and you'll end up with bumps and hollows, and it can compress the wood instead of cut it. With softwood it is important to swell the wood with water between grits in case you have compressed anything.

- when you're done test to see if you have gotten everything how you want it by wiping it with mineral spirits. Shine the brightest light you can find at your project right at the same level as the project almost parallel to the surface you're checking and look at it at the opposite angle toward the light.

- don't over-sand. On softwood 120 is probably fine. At a commercial shop where I worked we never went over 120 even on hardwood, and things looked great even with thin finishes, not epoxy.

- when you sand with your orbital sander, don't sand in one spot to get out the scratches or you'll create a low spot. Keep it moving over a large area until it's gone.

If you ever feel the need to read up, look at the Fine Woodworking web site. You can get a trial membership and look up their entire archive by keyword. It's really handy.

Now- it's done. What are you gonna do? Just paddle it. In a month you'll forget about it. I PROMISE.

Mike