Hi
Apple only accepts returns for purchases that have been made from Apple (whether online or in store).
Apple also does not currently offer either a trade-in program or an upgrade program for Apple Watch (not "iwatch").
I suggest that you return the Apple Watch to Sam's Club (subject to their return policy):
https://www.samsclub.com/sams/pagedetails/content.jsp?pageName=returns&xid=ftr:r eturn-refunds
And then buy your preferred Apple Watch Series 3 (GPS + Cellular) model from Apple or an Apple Authorised Reseller of your choice:
Note that you are not talking to Apple here - this is a user-based technical support community.