Cancelling stops your subscription from renewing - it turns off the next billing cycle so you won't be charged again. You'll keep full access to Balloon Plus until the end of your current billing period, and after that it won't renew.
To cancel the renewal:
Open the Settings app on your iPhone
Tap your name at the top
Tap Subscriptions
Tap Balloon
Tap Cancel Subscription
Once cancelled, you'll see the date your access runs through. You can re-subscribe any time before then to keep it active.