I finished my 2018 tax return a few days ago, concerning the 2018 tax return, is there a way for me to file them electronically or do I have to mail them in?

 

After you file

A 2018 tax return can only be printed and mailed, it cannot be e-filed.

After you file

Did you use the Online version or the 2018 Desktop program installed on your computer?  If you used the Online version it is ONLY for 2019.