If you do make a mistake, the IRS and/or State authorities (if you are required to file a state return where you live), may reject your return and simply ask you to correct something (after which you can refile your return(s)).
If your return(s) get accepted and a mistake is found later by the taxing authorities (or even yourself; e.g., you receive another tax document in the mail after you file your return), you can always amend your return, which is not only free, but a relatively easy process.
Don't be anxious, take your time as you enter your information and ask questions on this forum if you do not understand something (we have many experts here with years of experience who will be happy to help you.).
