Check out your map against the view.
Sounds simple, but often explorers give up at this point. Don’t.
Confirm your ideas – validate your findings. Check that what you think you’ve found is what you’ve found. Cook drew dotted lines on the map when he wasn’t sure what bits connected to what. His mapping involved measuring where he was and then drawing in what parts of the landscape he could see, looking forwards and backwards to see what connects to what. When you look at his map of New Zealand you can see (you, with the benefit of satellite imagery) that Bank’s Peninsula is a peninsula and not an island, as Cook’s map seems to indicate.