I try to make screen of my setup, when I am back home.
Do not use that math expression, you have nodes asin and Acos for radians and degrees. Because you admited poor math skills i would recommend using degrees version, as it is used by rotators.
Some vector math first. Get your coordinates from pawn location and touch location in same coordinate system. Ie. if you touch pawn, its touch location should be around pawn. And make it all in Cartesian_coordinate_system
Touch events have flipped y axis, while actor location has not. So you need to multiply touch event Y value by -1. Also 0,0 of touch location is in upper right corner, while 0,0 for player is on top of pawn. That why you need to recalculate your touch location to same coordinates that player pawn is using:
Flip y coordinate of touch location, then do touch_location minus pawn_location.
At this point add print node to test if all numbers are right. Print out flipped touch location, pawn location, and resulting vector. See if all works correctly. This also gets more complicated because pawn locateion is in world coordinates, you need it in screen coordinates. There may be node that recalculates touch location to world coordinate. Yes it all gets messy.
When you have vector math correctly done its time for trigonometry.
Normalize resulting vector. add 2 nodes: asin(x) and acos(y), feed acos(y) to sign node, then multiply both results. It works so asin(x) indicates left or right side of screen, and acos(y) gives actual rotation, but its same for right and left side, thus need of sign from asin(x).