Here's how I'd do the shooting scoring system

-.5 for a FGA
+1.5 for a FGM
+2.5 for a 3PM

so if they miss you lose .5, they make a 2 you get 1.5 in your FGM and still -.5 for FGA and if its a 3 -.5 for FGA and +2.5 for 3PM and 1.5 for FGM