Day trips to Amphawa are often offered from Bangkok. Mostly on Fridays, Saturdays, and Sundays, when the floating market is held. The classic tour generally includes Mae Klong Railway Market
, a boat trip and the visit of one or two local floating markets. I would advise you not to go back to Bangkok in the evening but spend at least one night there to enjoy the evening atmosphere on the Amphawa Floating Market's canal and see the monks' alms offering tour by boat in the morning. You can book a hotel in Amphawa here.