Christine,

All of your questions on this subject have been written about exhaustively.
The article below was from a simple google search for Bands vs Chains elitefts.

https://www.elitefts.com/education/training/sports-performance/howtousechainsandbands/

I feel the best info is on Elitefts and obviously here.

To answer simply:

Chains and bends are both accommodating resistance.
They serve SIMILAR yet DIFFERENT functions.

I don’t feel they are largely interchangeable, but you can do what you did in a pinch.

Bands are pretty inexpensive and we stock them.
It’s a good idea to have your own incase the gym ones are in use.

IF we don’t have what you want in stock, elitefts will.

You made a good decision for the day.