That is way too high for humidity. A chick will drown in their own egg if it's that high. If it's too low, they can get stuck in their egg. I like to keep the humidity around 50% for the first 18 days, and then crank it up to 65-70 during the lockdown (last 3 days.)
Don't give up though.....just begin again! You'll get it next time!
OH, sorry, your title said Humidity. Now, that is too low for a temp. For chicken eggs, you need the temp to be 99 degrees. Not sure if your chicks will hatch.....there is a chance they may hatch late. Have you candled them?
Temp is 99.5 for 21 days is normal hatch. Lock down at day 18! Means DO NOT open the bator even to add water. 90 is WAY too low!!! If its a still air ( no fan) 100-102 is fine. Humidity should be 50-60% for 18 days then crank it up to 65-80% until hatch! You can do a search on here for incubation rules.
ok geeze..i made another typo...lol..i DO keep the temp at 99...i have nothing to gauge humidity,,,after first failure i bought a turner...and used it...i havent tried again yet as i lost most of my hens to a predter....i have 10 chicks i bought and keepig pened up..and lost 2 to my grandsons getting into them...i will get a gauge for humidity before i try to hatch eggs again...i have refortified the coop now...so when my chicks grow up they will be safe..i have 1 big rooster who free roams at day...and roosts on the porch at night...not sure where the hens are roostin...im learnining but its been a chore and more to it than i thought!