You done good...maybe real good. What kind of grass do you have? Please tell me it is Kentucky bluegrass. KBG will fill in your cracks for you and will not have a different look. If you seed with a new mix of fescues, it will look like a checkerboard until you get it all turned into that type of grass.

If you did not roll the sod down, now would be a good time to do that. Roots will not grow across an air gap to reach the soil. Rolling will ensure the bottom of the sod is on top of the soil.

Keep it moist as if you were seeding. Water 3x per day, breakfast, lunch, and dinnertime, for 10 minutes each time. Do that for 3 weeks and start to back off. Eventually you should be watering for as long as it takes for the grass to survive a full week or more. For me that takes 4-5 hours per zone. Your mileage will vary depending on heat, humidity, wind, shade, sun, grass type, soil type, mowing height and some other factors I can't remember.

Do you have before and after pictures to share? I am a proponent of removing topsoil when it gets out of hand.