Counting the days wrong isn't that unusual, it happens a lot. As a result a lot of eggs get locked down a day early. Usually it is not a big deal, the eggs still hatch as they would if lockdown was a day later.
You want to say "1" when the eggs first go into the incubator or under a broody hen but an egg does not have a days worth of development until 24 hours later so you say one the next day. A good check on your counting is that the 21 days are up on the day of the week you set them. If you started them on a Tuesday the 21 days are up on a Tuesday. It's not that unusual for eggs to hatch a couple of days early or late so the 21 days is a target, not a law of nature.
Turning is not an issue. You can stop turning them a few days if you wanted to, after 14 days of development they no longer need to be turned. It doesn't hurt them to be turned, they just don't need it.
For the eggs to hatch they need to lose a certain amount of moisture. Nature was kind enough to give us a pretty wide range of what is OK. When you raise humidity in lockdown the rate of moisture loss is reduced, but the majority of time that doesn't have an effect on the hatch if you lock down a day early. Usually you are already in that good range.
There is another factor too. Each egg is different and loses moisture at a different rate for different reasons. If you go the exact 18 days some may lose moisture so fast that they are verging on the dry side. Some may be so slow that they may still have a lot of moisture. I know I'm overthinking it for you but it's highly unlikely any egg will be affected by you locking down early.
Totally normal. The 21 days is a target. For different reasons the eggs can hatch 2 full days early or late under a broody hen or in an incubator set perfectly for temperature. I understand how stressful this can be, but don't start to worry for another couple of days. I know, easier said than done.
