How can I edit or fix and put myself as a dependent? I accidentally marked myself as independent/I didn't answer the question. I'm worried it'll affect parents' taxes.

Did you already e-file?   If you already e-filed and answered that "dependent" question wrong, your parents' return will be rejected when they try to e-file.  They will not be able to e-file at all this year, and will need to print, sign and mail their own tax return that claims you as a dependent.   

If you have NOT e-filed then you can go to My Info and change the way you answered the question about whether you can be claimed as someone else's dependent and say YES that you can be claimed.  If you already e-filed, and your return has been accepted---the damage is done for now and you cannot fix it yet.

If your incorrect return is accepted you have to wait for it to be fully processed by the IRS and then you can amend it using a Form 1040X---which will not be available until March 26 at the earliest.   You can post back here for more help with amending when you are ready for that.

This is an unfortunate and common error made by young inexperienced tax return filers who are doing their own returns.