You can limit the total number of responses that you would like to receive on any of your forms.
On the Basic tab (default opened tab) of your form Settings page, there is a Want to limit received responses? option. Fill in the total number of submissions you would like to receive in this field, ensure you type in only valid numbers (e.g. 500, 2500, 350, 70, 120, e.t.c).
If you would like to accept more/fewer submissions than you earlier set, you can always increase or decrease the number from the Number of Submissions field. You can also clear the set number on the field to remove any submission limit.
Once, your form has received the set number of responses, your form would no longer be able to receive new responses and anyone who access your form would receive a ‘Number of expected responses exceeded’ error message.