What happens if I go over my submissions one month?

As of now I don't see me needing more than 100 submissions but if for some reason one month we go over what happens? Do we get cut off or are we just told that can't happen again?

Your account will go into Overlimit Status. When in this status all the forms will not be able to receive further submissions. Every time the form is submitted there will be reminder message that says not able to submit form due to over quota.

Reaching the Overlimit status will not block your account. You can still login and view all forms and existing data. You can update/edit your forms as well. 

In case you are not aware yet, there is a monthly submission that occurs every 1st day of the month. The reset will set your submissions counter to zero(0) again and will enable submission on the forms again.

User guide: https://www.jotform.com/help/408-Understanding-Your-Account-Usage-Limits