If you did manage to transmit the return, and if the IRS happens to reject your efiled return for some reason, you should be able to correct it and resubmit the efile, but it should be done as soon as possible.
Normally people with extensions who efile by October 15 and are rejected for some reason have until October 20 to resubmit without any penalty. However, in your case, if your efile date was October 16, you wouldn't have that grace period. But you should still be able to correct a rejected return and resubmit.
Let's hope that it was accepted in the first place. I told you some ways to follow it in my first comment above.