razer1980, I'm sure you already know what the best course of action is: Call or email the management and let them know what happened. It's up to them to decide and initiate the next step. If they want it back you should not be put to any avoidable trouble or further expense. This means they should collect it rather than asking you to take it to the post office or a courier.
There is not a person on earth who doesn't make mistakes, so not a single one of us can mount a high moral horse and claim title to the fruits of another's innocent mistake.
It matters not a jot whether the supplier is small or large, rich or poor, terrestrial or alien.
The moral decision is yours to make. Treat others as you would have them treat you. As you weigh, so will you be weighed. This is a test of your character, not theirs.
Follow your informed conscience, do the right thing, and let them know.