How can I make more than two choices in a text box?
Not with text box choices. Text box choices only allow two choices, so if you need more choices you must chain together more than one choice.
It is possible to create a more complex choice menu using plotscripting. Usually this is done by displaying a backdrop or text box listing several options and waiting for a keypress or by teleporting to a menu map where the player can move a cursor to select an option.
Note that you can use the figures and plotscripting to offer several choices to the player, but it is probably easier to make your own menus.