Hi, @DebMorr, welcome to the community, allowing you are using a "Fitbit" band and not a third-party band from somewhere like Amazon your band should attach firmly. It's possible you may have grit or something else preventing proper engagement in the slot so I suggest you wash it with warm soapy water to make sure it's clear. You may be interested in this video from 17.03 to 17.39 that demonstrates the process of engagement. Let us know how you get on.
I hope this is helpful.
Cheers
Gr4ndp4 | UK
AWAKE! for morning in the bowl of light has cast the stone that set the stars to flight.