I am trying to amend 2018 state and federal but it was rejected by the IRS so there is no .taxfile to upload in order to amend. Am I better off just starting over?

If your return did not get accepted in 2018, it was not filed and there is not need to do an amendment. 

See this TurboTax FAQ for help with amending

you can't amend a return that was not filed.

Just send in your correct Form 1040.