It really is best to wait for the refund, in case it is adjusted. You can extend your time to file so that you can be a little less stressed by filing this form (by mail): IRS Request for Extension.
Once you receive your refund your amended return will reflect the difference between what you received and what you should have received - this is another reason why it is important to wait. You will return only the part that is more than what would have been the refund on the amended return (if anything - sometimes the IRS ends up owing you more money instead.)
Your state tax return can be amended if necessary after you prepare the federal one - you will need key information from it to update your state return. It is possible that it will not require amendment.
You have filed a return so you will not be subject to any penalties for late filing. You could potentially owe a little bit in late penalties and interest for any late payment but if that happens you can often have the penalty portion removed with a simple phone call to the IRS asking for "First Time Abatement" penalty relief.
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