Size and accuracy of Apple Watch

I bought an Apple Watch 42mm. If I lose weight over time from working out and my wrist gets smaller, will the size of my wrist affect accuracy of the watch? What other problems could come? ...or would there be no problems at all? I'm already on the last hole on my band. Should I switch to the 38mm or will a simple purchase of a smaller band be good? Any and all answers will be appreciated! Thanks!