I am assuming that the problem is that the scroll bar on the right of the screen (together with its up and down arrows) is too narrow and your finger overlaps the list of books. Ignore me if I have misunderstood
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If so, it is a common problem with traditional desktop type applications on small touchscreens. I don't know of a way to widen it in Calibre (but I am no expert with Calibre) and can only suggest moving all the inhabited columns in the display of books to the left by narrowing them up so that you end up with white space between the right-most column and the scroll bar.
I cannot test this myself, but you may also find that if you have the User Interface Style in Preferences>Look and Feel set to Calibre Style then you may get a better result if you change it to System default. Also, if your screen responds to a pointer then perhaps that could be used (but inconvenient).