I created a homebrew spell called, "Mind Blast," 0 Level spell. Having issues with it automatically being part of the arcane domain Cleric subclass. 

Did you list that specific subclass as one of the spell lists upon which this spell appears? If so, that’s how prepared caster subclass specific lists work. If not, post a link to the homebrew so a Mod can look at it for you. They can view even unpublished homebrews.

I'm not sure what I did wrong, I'm new to homebrew creation on here.

https://www.dndbeyond.com/spells/662183-mind-blast

arcana domain is on there maybe you accidently put it in so just go back and delete it

You can also delete Arcane Trickster as well since they access the Wizard spell list.

I've already published it, so I disabled it for now and am just gonna recreate it

You have to hit “create new version.” Then you can edit the new version and re-publish it and it will overwrite the old version. But it will leave a ghost of the old version in your homebrewer.

In future, don’t publish until you’re sure it works perfectly.

Thank you, I'll keep that in mind in the future.