How can I create a checkbox with one option, and unselected

I need to create a form which has tick boxes (some required, some not). These need to be set to show unticked and are only a single box, not the three as standard option. Currently, I can't set the tick box to be unticked.

http://www.jotform.com//?formID=50363017972959#

In order to achieve the desired result please
1. add a checkbox field
2. remove the label, by double clicking it
3. Click options and add the preferred text
4. Click selected and choose the unselected option:

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