I have had this happen to me when I was newly qualified and I felt truly awful.
So now I am extra super special careful when checking peripheral IV sites.
Even though it takes forever I take the splint/backboard off at every check, also tight t shirts or name bands can mask infiltration/extravisation.
I always set my I've pump pressures on the lowest they can be set. Which does mean I am constantly silencing alarming pumps when babies wriggle but I'd rather that than miss something.
I find feeling the site more useful than just eyeballing it as puffiness feels different to Chubby baby arm
and you can also feel for hardness or coolness.
And like the previous poster said comparing the two hands or feet is always helpful.
Don't be hard on yourself lines can go quickly and it may have been fine all day until that last check at handover time.