Thanks. Looks like Go is a web version only and doesn’t support curves. Fortunately I have two weeks to get out and get a refund.
A little research led me to Alibre Atom 3D which looks like it will get the job done.
…… and it’s less money 
…… and I get to own it
……. and I have 30 days to return it
……. and it was on 50% off for Black Friday sale

The early bird gets the worm but its the second mouse that gets the cheese.