Cut your grass at the highest setting for your mower. You're not supposed to cut more than 1/3 of the height of the grass at a time but I doubt your mower has a setting for 8 inches high. So do it as high as you can and then in a few days cut it again to the length you'll be maintaining. I don't know why some grass hasn't grown. Maybe it was later in germinating and then had higher grass all around it shading it. You should have been mowing as soon as the grass was one inch over your target height. I have new neighbors across the street who planted grass (overseeding) and they have been watering every day but they haven't cut it and it's all floppy. I don't want to offer them unsolicited advice, so I haven't said anything to them about it. But I have been wondering why on earth they're not cutting the grass.

Thanks beckybeck! I'll cut it. Maybe the tall grass it blocking either sun or water from the sprinklers from hitting the low grass.