OK got it .Get something smaller for your floor like quarter inch wire cloth stainless steel if you can find it. You have had two problems heat and humidity .I don't know how far you have progressed with the assist at this time but the reason your have a twenty four day egg that is still alive is your temperatures have been low for the entire incubation . Shoot for 101.5 to 102 .102 being the max . The range is 19 to 25 days for normal size eggs . I'm quoting from a UCONN college text that is forty years or more old . Incubators have become more efficient and the average now is 19 to 23. days . But that is just an average . And remember that it is absolutely a must that those temperatures are taken at the top of the eggs .
If it hasn't internally piped What ever you do don't break the inner membrane . Ever time I've done that it was instant death for the chick . the ladies are much better at assisting than I am. I break them out with a chisel . Good luck I hope your chick makes it . And the egg sinking doesn't matter.