Hello, Kerry-Marie.
Thank you for using Apple Support Communities.
From your post, we understand your text messages are muted when trying to dictate messages. We'd be glad to help out. To clarify, do you hear any sound from the Apple Watch or is it just the messages?
Does Siri work as expected? Try some of these steps to help check to see if your microphone is working as expected: Use Siri on your Apple Watch
Make sure both the Apple Watch and iPhone are update to the latest software version:
Update your Apple Watch
Update your iPhone, iPad, or iPod touch
Keep us updated.
Cheers!