Depends on when you filed your return, usually within 3 weeks is the normal return, but if you had a dependent(s) or had a lot of additional tax credits could t...

If you have already filed it is too late, the IRS has already received your return, if not just sign out and go somewhere else to file

As long as you entered in all the correct w-2 information and claimed nothing else or got any additional tax credits that should be correct.

Yes as long as you are the primary signer and owner you should be able to, in the tax break section it should have a section about big purchases or car credits ...