If you're willing to put more time into it, here's how I fix that kind of thing:
1. Get some JB Kwik.
2. Mix a little bit larger amount than you need.
3. Wait. Not too long, mind you. But, maybe, a minute until it has gotten to a tacky texture (for other things, you wouldn't wait at all). You don't have a lot of time here, since you've already let it harden part way, so be quick.
4. Using something completely solid, straight, and flat (I prefer popsicle sticks), spread it over all your little "dents" and bits that look funny.
5. Scrape it off with the flat side so that you have a fairly flat surface, with just the JB Kwik in the "valleys." If the valleys turn into "hills" then that's fine, but you'll have more to sand off.
6. Wait until it hardens (15 minutes or a bit longer for mostly-hard).
7. Sand it by hand. Use a fairly gritty sand paper at first, to remove most of the excess. In this mostly-hard state, you can even remove some of it with a fingernail (if you've gotten some on an area that didn't need it, for instance).
8. Look it over, if there's any places that need more filling, repeat from step one. If necessary, add a coat of paint to help highlight the problem areas.
I know that you know pretty much all of this, SS, but I figured I'd type it out for anyone else who might find it useful. Basically, my suggestion is "use JB Kwik." I really have a love/hate relationship with that stuff. It's versatile, but can take a bit of trial and error until you get know how to use it just right. It's messy as Heck, smells, and is and toxic. So after you're done be sure to wash your hands straight away. It can do funny things to your skin (at least, my skin) if you get a sizable glob on you.