Yes you can certainly add text to the spine of your photobook!

To do this, click to add a text box to the page.

Double click in the text box to change the text.

Click somewhere else on the page, then click once on the text box.

You will notice a green circle in the top left corner of the text box. Click on this green dot and drag it clockwise to rotate the text box.

Once you have rotated the text box you can move it to the middle of the page where the spine is.