Your screenshot shows a perfectly normal Print dialog which is supplied by the print subsystem of the OS. It's merely intended to provide an indication of how the content will appear in print. It is not a scalable window. Neither can the thumbnails be enlarged.
If you want a larger display of how the content will print go to View> Page Layout in the Excel menu bar. Page Layout view also can be selected using the Page Layout tool on the View tab of the Ribbon as well as by using the View Shortcuts at the right end of the Status Bar:
You may find Page Break Preview to be useful as well.