If there was too little humidity the eggs would actualy shrivel up and look dry.
Dont exactly know what you mean by "harder".
The eggs should look like what they did when they were laid, which is white, of the right shape and tight, so when you lightly press on an egg it shouldnt cave in and stay caved in when you remove your finger.
The eggs should be fine if they are still of a good colour (They will change colour during the incubation process, closer to the end you will think they are starting to look a bit more seethrough.), have no mould and just look like normal.