Long and short of it. My bathtub’s spring stopper has deteriorated. Building manager solution was to use a rubber stopper. I looked for a replacement part, couldn’t find one outside of an outright replacement. So I modeled and printed this one in TPU.
It works!
Increasing the width likely won’t help a ton. Your layer lines are the issue. Unfortunately, TPU can be a bitch to finish.
I’d put a layer of something over it to smooth out the surface. Flex seal would probably work, or maybe some firm silicone epoxy.