Sadly, currently there is no way to view used resources on an OnDemand instance. If you do end up nearing your limit, you should receive a notification from Atlassian.
If you're running into issues creating a backup of your instance, I suggest that you contact support directly, and they'll be able to assist you further:
Hi my Community friends! For those who don't know me, I'm a product marketer on the Confluence Cloud team - nice to meet you! For those of you who do, you know that I've been all up in your Co...
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