Is the price at which the land was sold, being more than what was agreed upon, considered void, and must the extra money be returned to my friend, and if I am unable to return it due to my shyness towards him, is it permissible to give it to an orphanage or a charitable organization?

If you agreed with someone to sell a piece (of land/item) at a specific price, and then you sold it for more than that, the sale is valid. However, you must give your friend the full amount for which you sold it. You are not permitted to give the difference in price as charity because it does not belong to you. You must also repent to Allah.