Hearing my own voice is throwing me off. Can I mute myself to myself?

Listening to my own voice on a slight delay ruins my ability to speak coherently. Is there anything I can do so that I can't hear myself talking?

This usally happens because you are using an open mic and not a head set and you are getting reverb from your speakers.  Though thats not always the case, we would need to know more about how you are setup, head set, mic, discord, roll20 web and video..etc.

If it's coming from another player, you will have to get them to fix their setup. Cheap headsets often get microphonics transferring through the plastic from the speakers which will give all other players an echo. You can check this by muting them all, talking to see if it happens, then unmuting them one-by-one to find the culprit. If it's not the other players it's your setup, as Mark has said above.

I'm set up with a Logitech H390 headset, going through Roll20.