Keep hitting the ball out of court when using your backhand? Do you feel that you are not quite able to complete your follow through? This is a situation that happens often in tennis, are you are stopping your racket at impact point, this might be the cause of not being able to hit your target.
Knowing you are not quite doing the correct thing is a bonus, so with a friend ask them to watch how you play a double handed backhand in match play. You will then have a second opinion of how you play, and it is now time for you to become more specific about your backhand. Your friend has confirmed that you are stopping your follow through at contact point; this is a common problem for a great many people.
So let us set up a practice to help you develop your follow through, set a challenging and achievable goal. The goal being to "extend out in the direction you are hitting the ball, then smoothly bending your elbows and wrapping the racket over your shoulder."
Ask your friend to monitor and help you evaluate your practice. An example would be to set a weekly target, write down the day and date you are going to assess your improvement. Your friend can write down on a piece of paper the headings, Completed follow through or did not complete follow through. Put a tick under the heading which you did, and then analysis and discuss your next options. The improvement you make will depend on your desire and how well you set targets for your goals.
Your feedback and analysis came back with more ticks on the not completed follow through heading. Next move, talk to your desire and work on putting more ticks on the completed follow through heading. Easier said than done! But with your desire and commitment, how can you fail to develop your tennis. Have fun and enjoy your achievable challenges.