If you post a code snippet, ALWAYS USE CODE TAGS:
How to use code tags: Using code tags properly
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When you compute a “delta” between two vectors, such as where you compute shot, you always want to be “destination minus source,” but you have inverted that above.
Additional interim variables can also be helpful, like this:
Vector2 playerPosition = transform.position; // lops off the Z, making it zero
Vector2 shot = screenPos - playerPosition; // always subtract source from destination for directions
Of course, if the above script is not physically precisely located on the player’s “shooting base transform” (eg, his finger or gun muzzle), all bets are OFF.