Here is how I made it much rounder,
- Load the STL into Tinkercad.
- Add a ruler to the workspace and choose the option to measure from center.
- Center your stl and lock it.
- Add a tube from the right menu and center it as well.
- Set the number of sides on the tube to 64.
- Increase the diameter of the tube so that it is slightly larger than the original STL (this may take some experimenting.
- Download the mode and confirm that you have successfully trimmed the model.
- Print the model. A rounder model is easier and less jerky for the printer.
Here is what my screen looks like after completing the above steps. The important parts are underlined in red.