Your AWS account will be able to provision up to 64 vcpus for all AWS instance types including GPUs. You can use the following directions to view their credit:
The Startup Quick Guide to Managing Budgets, Credits, and AWS Resources (amazon.com)
If you overspend or your account gets compromised before a billing cycle (end of the month), you are expected to submit a billing support case ID with AWS Customer Service ASAP and ask for a billing adjustment. The decision to approve the billing adjustment is only with AWS Customer Service. If a billing cycle has passed, you will be responsible to pay the overspent amount.