@Nathan Lomax The error messages talks about not enough instances being available to satisfy your request. Instances are the VMs. The region you are attempting to deploy to likely has a high number of new web apps being created and thus, supply is having a hard time keeping up with demand.
To get around this, you can try deploying a different size App Service. If you are deploying a B1 instance, try to deploy an S1 instance.
More than likely, you will need to attempt a different region. If you are currently trying East US, try East US2 instead to see if you have better luck.
Those are your two best options to get around this. Thank you for your understanding.