Well, look at it this way, everything is practice. So why not try fixing it up, but if you aren't 100%satisfied with the results, cut the whole lot back. There's what sounds like (i haven't tried it) a very interesting technique described hereabouts for using water soluble filler around a run so you can sand more accurately.
There's another thing I'd add from experience with boatbuilding. People always feel they have to go right back to bare wood, but the paint manufacturers don't advise it in general. They suggest just sanding back to good paint.
So if you sand back give it no more sanding than you need to go flat.
Having said all that, it rarely does any harm to get an extra coat on, just don't sand back to excess. Is it much more work to do a whole coat than patch?