Import curved objects into TinkerCad

Hi all

I have been using TinkerCad for a couple of years now, generally with a degree of success.

However, one issue I keep coming across is how to import curved shapes into TC properly. Typically when I am starting a design I start with a flat shape designed in Adobe Photoshop... I save it as a black and white JPG. I then use an online converter to convert it to an STL file and then import this into TinkerCad... but more times than not any smooth curves are imported with jagged edges sometimes zig-zagging into the solid part. So far my work around has been to delete the imported image all except a very thin slice, 0.1mm or thinner, then stretch this to the height I need - while this usually works I am sure its not supposed to be this hard to import smooth curves / text / logos, etc.

Can anyone advise what I am doing wrong and the best way to do this?

Thanks