howdy, here’s a recent answer to that question:
there isn’t an automatic way of preventing it from scaling - we feel like simply shutting the form down after 100 on our side is really bad UX - especially as most people use forms for sales-y purposes of some kind, even if its just lead generation.
You could, I suppose, create some javascript that counts, and does an action to de-activate the form after you hit 100, but again, that might not be the experience you want for your customers - your call! 