Utter Failure

I've been hesitating to post lately because I'm just so embarrassed by how bad my seeding project has gone. As you can see in the first picture, there is some green to be seen, but to be totally honest, most of that green comes from weeds.

There are some tufts of grass in the area, but they are few and far between.

There is some grass inside this dense thicket of weeds, but it's hard to see.
And some of the area looks like this: brown grass left over from the initial kill using Roundup.
So what happened? I hardly feel like I'm qualified to even guess, but I have some theories. Some may be accurate and it's likely that several came into play all at once.
1) I planted too late. I did get a bit of a late start, but the weather was very spring-like when I planted, so I thought I'd be safe. It got hot a couple of weeks after I planted.
2) Some seed may have washed away after a hard rain that hit shortly after I seeded.
3) Poor preparation. I thought I did everything right, but if I had to guess, I'd say that I did a poor job getting good "seed-to-soil contact." I just don't know how hard you are supposed to rake things up. I was concerned about pulling all the seed to one spot as I raked, so I wasn't very vigorous in raking.
4) Bad seed. If you'll remember, I mixed some pure Kentucky Bluegrass seed with a mix I bought this year at the store. The KB seed was purchased last year and it's possible it didn't germinate.
5) Lack of water. I did try to water twice a day, but I wasn't as consistent as I should have been. My underground sprinkler system has a short and I have to manually start the sprinklers. Some days I may have not let them run long enough.
So what to do now? I'm hesitant to spray weed killer on the area (at least it's green!) because, even though the grass is six weeks old, it could kill the new grass too. I'm also not sure that I want to keep watering this mess through the dog days of summer (throwing good money after bad). What I may do is string it along and over-seed in the fall when conditions should be better. If I do that, I'll be stuck with the embarrassment for the entire summer!
As I've said many times, I am no expert in lawn care. That's one reason I started this blog. I wanted to consult experts and help others like myself who are a bit clueless about getting a green lawn. If this had been a real medieval quest to slay a dragon (instead of weeds), I would have tripped on my sword on the way out of the castle and impaled myself. Oh well, there's always next growing season!