ps please do not keep opening the incubator , to candle. Every time you open, it looses humidity. The chicks can end up "shrink wrapped,"- very difficult to hatch out then.
I have never incubated eggs either but, I have heard when they go past 21 days, its generally because the temps were lower than optimum. So please give the others some time don't rush to throw them out.
How is the chick doing that did hatch?