More than likely you need to just go into practice mode and work on your shot release timing. But in your defense the CPU does seem to hit a lot of questionable shots. You really have to mess around with the sliders to find a good balance when it comes to authentic NBA style gameplay.
Try....
Inside Shooting: 50
Med Shooting: 40
Three PT. Shooting: 30
(For both User & CPU)
This will mimic real life as inside shots have a higher % of going in verses a lower % 3pt shot..... in other words your chances of hitting should increase the closer you are to the basket.
EA has all the shooting on 50% which is not realistic at all. It shouldn't be just as easy to hit a 3 pointer as it is to do a layup....
Also try to turn the Shot Contest Impact slider up to maybe 60-70 this will allow your defense to have a greater effect on the CPU's shots. But you will still have to play great defense in order to see results. You'll have to work on playing good defense without fouling.... Also while on defense the LT button or (Left Trigger) is your best friend. It will help you stay in front of the person you are guarding. Remember the key to good defense is to just make the offense take the hardest shot possible. You're not going to stop the CPU from scoring all the time... but you can make their shots much harder.