If you want to send your form after your visitor checks a checkbox, you can take advantage of the validation functionality for Text fields, so please define your field as the Text attribute type (instead of a boolean) and then follow the settings below:
Form control: Multiple choice
Repeat direction: Vertical / Options (one value;name pair on each line - example: 1;Blue)
Data source: yes;I agree
Regular expression: yes
Error message: You have to confirm this form
-jh-