of course you were not wrong in accepting the offer. I'm curious what your original fare basis was because normally you would purchase up to the next fare available that would waive that Sat. restriction. The res agent was obviously trying to accomodate your wish to get home earlier. So long as any changes made to a file by res or ticketing are commented correctly then checkin agents really shouldn't be second guessing and hassling you. They should be smiling as they hand you the boarding pass and wish you a safe and good trip.
That's what most of us try and do. Stay away from the few sour face agents and try and time your checkin line to get the ones that are chatting and smiling.
Glad you got home early.