You're fine to use third-party assets in your project, though they will need to be licensed/attributed appropriately, either in-game or in documentation as required.
This is pretty clear-cut for visual, audio and other non-code assets, but can get a bit murkier with external code and scripts. As you're being assessed on your coding ability, you need to make it clear what you've used in addition to your own work. If it becomes difficult for an assessor to identify what you've actually done, then this may cause an issue.