There is a problem with just seeding with fescue. Fescue grows in little clumps. It is called a bunch grass. Kentucky bluegrass grows and fills empty space like a moving carpet. It is called a sod forming grass. Many people mix the two grasses for the various benefits of each one. Since you planted fescue you will only have one little grass plant for each grass seed. If you want it to become more dense without adding KBG, then you need more grass plants (and seeds).

Now is not the time to seed for the reason mentioned above. An alternative is to lay sod, but that gets expensive very quickly. If you can wait and maybe tolerate some weeds this season, then the late summer to fall is the time to renovate. I would try to sit on my hands and read all I could here and elsewhere about caring for lawns. Then when the summer heat breaks, spring for some good seed and get to renovating. Folks here can help you with that.