Check out HubSpot Academy's FAQ here. You can also ask questions about your certifications by going to this discussion board on the HubSpot community or to contact HubSpot Support.
It's worth noting that most issues that students confront when trying to complete certifications is that they do not have proper permissions. Essentially, this means that features of the software are locked to them, so they cannot complete exercises. To check if you have the correct permission, check here