the screen seems small. Definitely not 12.9 inches across. Is their a bigger screen foe the ipad pro?

Screens on iPads, like other devices and televisions, are measured diagonally. The iPad Pros currently sold are 11" or 12.9" -- see" iPad Pro - Technical Specifications - Apple

The 12.9" is the largest model available.

Screen sizes are always measured diagonally between the screen corners - e.g. measuring diagonally between the upper-left and lower-right corner of the screen…

2021/2022 iPad Pro 12.9”

20121/2022 iPad Pro 11”

You should also note that that the corners of the visible screen are slightly rounded. The diagonal screen measurement will be to a the corners of a “normalised” rectangle - this being slightly larger than the measurement between the rounded corners.

You can compare all the major specifications and physical dimensions of iPad models here:

iPad - Compare Models - Apple

Like any TV screen or video screen, the 12.9 inch dimension is measured on a diagonal, this dimension being the longest dimensional leg of a triangle.