Filing before you have all of your information causes you a lot of aggravation that could be avoided if you just wait until you have everything first and then take your time preparing your return so you do not mess it up because of a rush to get a refund.

You cannot change or add anything on the return that you just e-filed, nor can you stop it.  It is too late, just like when you put an envelope in a US mailbox on the corner.

If you left out a W-2, or a dependent, or a 1099 etc…DO NOT change your return while it is pending.  The changes will go nowhere.

Now you have to wait until the IRS either rejects or accepts your return.  If your return is rejected, you will be able to go into your account and make the necessary changes to your tax return and re-submit your return.

 If the IRS accepts your return, however, then you have to wait longer until it has been fully processed and you have received your refund.  THEN you can prepare an amended tax return and mail it in. You have to be able to work from that return exactly the way it was when it was e-filed originally.  You will need to use a form called a 1040X. You cannot e-file an amended return.  They have to be mailed, and it takes at least 2-4 months for the IRS to process an amended return.  Meanwhile, DO NOT go in and start changing anything on your return in the system, or you will make a mess for yourself.  Sit tight and wait until you see what the IRS does with the return you just e-filed

Can I cancel an Efile?

No. Once you click that big orange TRANSMIT MY RETURNS NOW button, you're done. Right now, the status of your e-filed return shows PENDING and there is nothing that you or anyone else can do at this point. It's going to remain in pending status until Jan 27th when the IRS starts processing returns. (Assuming there's not a delay that causes the IRS to change that date)

If your return is rejected by the IRS, you'll get an email notifying you of that. When rejected, it's as if you never e-filed it. You can just make your changes and re-submit it to the IRS.

If your return is accepted, then you have to wait until the IRS has processed your return. Your return is not processed in it's entirety until you have received your refund. At that point you will have to file an amended return to make your changes.

An amended return can not be e-filed. The IRS says so. You have to print, sign and mail the return to the IRS. Amended returns can take 6-12 weeks or longer to process. If your amended return results in a refund or additional refund, the only way the IRS will pay that refund on an amended return is by mailing a paper check to the address on that return. So you can expect to be waiting 12 weeks or longer before you get it.

This ie exactly why I recommend people "NEVER" e-file their tax return until march 1st at the absolute earliest.  Now, depending on your specific situation, you could be waiting months to get your refund.