If you still have issues with scoring penalties in FIFA 17 be sure to check the following tutorial:
Change your starting position
Before you step up to the spot, the first thing you’ll decide is your starting position. You’re now able to choose to take a wider or straighter run-up by moving the right stick, as well as lengthen the run-up by moving the right stick backwards.
The angle and length of the run-up affects how you’ll approach and strike the ball. Longer run ups will increase the power on the shot, letting you smash the ball into the back of the net.
Once you’ve chosen your starting position, hold the left stick up to begin your run-up. You can modify your approach by changing its speed or by adding a stutter to your run-up.
How to stutter: To perform a stutter, tap LT/L2 as you approach the ball, a useful technique if you notice the opposition ‘keeper timing their dive to your approach.
How to slow your run-up: To slow your approach down to give yourself more time to adjust your aim and perfect your timing, hold LT/L2 for the duration of the run up.
How to speed up your run-up: To speed up your run and increase the power with which you hit the ball hold RT/R2.
Aim a penalty just like you would a regular shot in gameplay. As you approach the ball, aim by tilting the left stick in the direction you want to send the kick, and use B/Circle to add elevation and further power. Be careful to balance the risk and reward of aiming for the corners, as pushing the left stick too far to either side or holding B/circle for too long will see your kick miss the target altogether.