Touch screen friendly combo box

Hi,

I have a register that has my students down the left and the date up the top. There are combo boxes on the spreadsheet so that I can click the arrow and select if they are Present, Paid Online, Paid but not present etc. I am using a touch screen tablet and it's hard to select the arrow. How do I make the whole cell clickable to show my options instead of just the arrow. Also, how do increase the size of the contents?

I am an absolute noob so go easy on me!