After you file

I went through the process of filling a tax return as if i didnt file them yet. Federal said I got back $600+ dollars more. I filed like anyone else would file. How do I file an amendment so I can go ahead and file through them? Do I have to wait until state comes back? If Credit Karma is scamming what are some ways I can tell so I can get back the correct amount that is owed to me. I mean that is a lot of money that would be owed if it isnt a scam, correct.