Oops how to correct a mailed paper tax return

[redrosepro]

I am a non resident and I mailed my tax return T1, but after sending it I realized I made an incorrect calculation of cost basis that goes into Schedule 3.
Now how do I correct it please?
If I resend the corrcted returns, the CRA will get two on back to back days.
Or should I file a T1-adj already?
Or should I wait till they process it, find the error and then reply to me ?

[nelsona]

You never refile a return. You file an amendment (104X) for IRS and a T1-ADJ for CRA.
They can figure it out.