Regarding storage consumption, it may take up to 24 hours for your data cleanup to reflect in the storage reports. I would check back in a day to see what it looks like then. If you still need to clear up space, you can try following some of the guidelines at the reference below to help free up space. Do keep in mind that even if you reduce it to less than 1 GB, each environment still consumes a minimum of 1 GB of your storage quota.
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You can't reset default environments and unfortunately it will consume your 1gb database capacity for the per app license so you won't be able to create an additional environment unless your purchase more capacity.
For this reason I always recommend at least one per user license or one dynamics 365 (sales or service) to unlock the higher capacity limits.