The offer I see states this:
Offer expires on April 24, 2025. Offer for eligible new and qualified returning subscribers redeeming on eligible Apple devices or where a subscription to Apple TV+ is billed directly through Apple. Offer not available if (i) you are eligible for a three months free Apple TV+ offer or (ii) your subscription to Apple TV+ is billed through a third party or your mobile wireless provider. Other new subscribers may receive a 7-day free trial. Plan automatically renews at $9.99/mo. after offer period until cancelled. Terms apply.
For those that are eligible, you can accept the offer on the page here:
Get Apple TV+ for $2.99/month for 3 months - Apple
You have until May 1st to continue to watch because the subscription is still active since you have already paid for that month. After cancelling it will now just no longer renew and will then become inactive after that date.