Don’t worry and don’t beat yourself up about it :hugs
I’m glad to read the chick is out and doing ok. Still time for your other eggs as 21 days is just a guide.
That pip looks fine and the chick should be getting enough oxygen through there. As it’s missed the internal pip out of hatching it is likely to take longer to hatch. They can and do hatch from wrong end pips though. Just incase there is some info here ~ ASSISTED HATCHING