I'm located in southeast Pennsylvania and recently seeded around a new patio with Scott's EZ Seed. I'm getting things to grow, but I don't know if this is a weed or grass or the type of grass. I've provided the seeds that the Scott's EZ Seed contained along with a shot of the rest of the grass.
It's grass, I couldn't tell you what kind, but it's definitely grass. If you mow it, it will start to lead out lower to the ground. Start with a tall cut and work it lower through the season until you reach the height you want.
Most grasses "except clump grasses" can be trained to be mowed very low if desired, however the flip side is you need to water a short lawn because the grass doesn't shade the soil from the drying sun when it's short.
I cut mine the highest setting, it helps the grass stay green in the summer.