Stop reading right now, mow it short and bag it. New seed needs sunlight to take root. If you shade it out with tall grass or grass clippings, you hurt your chances for a dense turf. Hope for the best.

You might toss more seed if you have some left over. Be sure to roll it down or at least walk over it to ensure the seed is in contact with the soil.

That is the kiss of death for any kbg overseeding. You will definitely need to mow it. However, too much vacuum action and you will see a lot of seed in your bag--try reducing throttle. Your kbg seeds have a LONG way to go...you need to be diligent about mowing the lawn when you think it's too long. I would aim for no longer than 2" but you do what you can. Good luck to you in any case.

Thanks for the advice. I mowed the grass pretty low this evening. Now, I am wondering if there is any grass seed left. Should I buy more and overseed the whole lawn again?

Tough to say. Did you bag? If so, did you examine the clippings for seed. If you feel like an overseed is warranted, you may as well attempt to scalp the existing lawn and stress it to give you more time. If you really want to get as much of the new seed to "take", consider slit seeding which will expose more soil and thin out the existing lawn some. You should buy more seed if you do this but the seed you put down should still be good. However, many people report seeing kbg germinate at 7 days so you don't have much time.

Overseeding is very time consuming and costly. You definitely want to do everything you can to ensure success or quite possibly end up with wasted effort (I know this from having two failed overseeds for the same situation you have).

Yes, I did bag it and pretty much scalped it, but I couldn't tell if there was seed in it or not because there was so much grass. I don't mind going and buying more seed, but I was afraid that if there is still plenty of seed down, and I put more down that they would compete with each other and neither would grow. My fear now is that the existing grass will die since I mowed it so low, and the new grass won't germinate and I will have a big mess in my front yard.

Go ahead and reseed, at a lesser rate (about half?) of what you put down before: you'll feel better about it.

Don't worry about the competition. Plants compete with each other all the time: the strong survive, and they spread out.

You should know you're going to be looking at a disaster on that lawn. But here's the point: you would have anyway. We all did, and we all do, and those of us reseeding this year have all of that to look forward to, just the same as you.
At some point in the reseeding process, the old looks pretty raggedy, and the new doesn't look nearly healthy enough to be able to take over, and you'll think this can't possibly work out.

It WILL work out. It will look much better than it did. Take frequent pictures, from exactly the same location and view, three days apart, for the next 45 days. View them on the computer. View them as a slideshow, numbers one through thirty, and you'll see the incremental progress that lawn makes. It's slow. But it's kind of inevitable.

You'll be fine. Relax.

I doubt you mowed low enough to kill the existing lawn. Cutting low to stress it is desirable. KBG takes so long to establish, the existing lawn really is public enemy #1. You want to talk competition? Seedlings vs. established lawn is no contest!