Turning on Airplane Mode isn't Stopping Text from Being Delivered

Hello!

I have been trying to get around this for hours now, and I would really appreciate some help! This is my first time posting on Apple Support, so please bear with me as I try to offer as much information as possible.

Exactly two hours ago, I accidentally sent an embarrassing audio recording to someone. However, since I acted quickly, I was able to turn on airplane mode while it was still in the process of sending, and the bar went from blue to green.

However, two hours passed, and the audio recording is still in the process of being sent. It doesn't say that it hasn't been delivered, and I'm scared to turn airplane mode off and try something else in case the second I do the audio recording does get sent.

If it makes a difference, the bar is pretty close to hitting the right-side of the screen, but it's not completely there yet, and has been in that position for what feels like forever now. It says, "Sending..." at the top.

In addition to having kept my phone in airplane mode that entire time, I also restarted it (held down the lock button on top) which made no difference.

Also, Wifi and iMessage are disabled, though I turned on MMS Messaging to see if that would change anything. (It didn't.)

Please help me! How come turning on airplane mode while the audio recording (it was only a second long) was still in the process of sending didn't stop it from being delivered? (It's still in the "sending..." process.)

Any ideas as for what I can do from here?