Why not return it? I don't personally approve of people taking advantage of Apple's generous return policy (ordering one of each new Watch color/casing, for example, only to return the ones they don't like) but in this case, it seems that Apple should be held accountable: you bought a size 7 band (or whatever) and now it's a size 8, due to normal wear and tear through daily usage. You bought a size 7, and now you have a size 8. The product you have now is NOT equivalent to the one you purchased, through no fault of your own. The onus is on Apple to remedy the situation (in my opinion).
If Apple wants to sell bands so uniquely fitted to each person (sizing strips, etc) then they have a responsibility to ensure that the fit remains consistent for the life of the product, or at least until the warranty period expires.