I have 3 1/4in baseboard molding that I want to transition from to a flat surfaced bathtub/shower. What are the generally accepted options for doing so? I could cut it at a 45, 90 or some other option but I really have not come into such a situation before so I'm not sure what is recommended for aesthetics or otherwise. If it isn't clear, I do not want the baseboard on the shower/bathtub, I want to end it on the drywall.
I created mockups of a few different configurations and decided that I liked the look of the following the best. I created a 45°(an opposite cut of my original example cut; sorry I don't know the correct terminology), and created a "return" that was at the opposite 45° and cut 90° to butt up against the wall. I liked this option because it left no grain exposed and seemed to be fairly clean. I didn't like it because the final piece is so small and was difficult to cut precisely.
You could cut it at a 45, like you've done.
You could back cut it at 45, then glue in a small triangle of molding to fill the gap.
You could install an end block.
You could simply cut it at 90°, and leave it. Really it's up you your personal preference.