Is it possible that a photo went through without me knowing?
iOS will always tell you if a message is sent or not. It only won't show up if you delete the message yourself. Of course, there is always a chance of there being bugs, but this is unlikely. If you didn't hit send, there is very little chance it actually sent.

If you have a Mac or another iOS device, you can open up the Messages thread on that device to see if it sent.

In the future, if you accidentally send a message, shut down the device immediately, and when you power it on, turn on airplane mode. If you go to the message thread, it should show an error with sending the message.