The Triangle Pose, or Trikonasana, is a standing pose that strengthens the legs and stretches the sides of the body. The traditional alignment for the pose is to keep the hand on the ground, but not everyone is able to reach that alignment.
It's important to remember that yoga is not about achieving a specific shape or reaching a certain level of flexibility. Instead, it's about listening to your body and working within your own range of motion. If you are unable to keep your hand on the ground, there are several modifications you can make to the pose that will still allow you to reap the benefits of the stretch.
One option is to use a block or a rolled-up blanket to support your hand. This will allow you to maintain proper alignment in the pose while still being able to fully stretch the sides of your body.
Another way to modify the pose, is to keep your hand at your waistline, this way you can focus on the side body stretch and core stability.
It's important to work within your own range of motion and never push beyond what feels comfortable for your body. If you have any concerns or questions about your practice, it's always a good idea to consult with a certified yoga instructor.