Can I make the "accept terms" checkbox unchecked by default?

You can choose if you want the checkbox for accept of terms and conditions to be checked by default or if you want the user to tick it off actively.

Go to Edit campaign > Sign-up page

Uncheck the 'Opt-in checked by default' checkbox and remember to save and publish.

When the check box is unchecked, the sign-up fields are disabled until the users checks the box.