Mummayoga hello,
If your heel doesn't touch the ground its ok, they do have heel wedges just for this purpose. Also, its important to square your hips, so if your back leg is your left leg internally rotate it by coming up on your toes, then bring your right hand into your right hip crease so you can draw the right hip back left hip forward. tailbone is down as pubis is lifting so your in nuetral pelvis. navel toward spine Make sure your stance is stable so you may have to adjust your feet. In this pose you are not on a tight rope. Take a deep inhale raise your arms up as you relax the shoulders exhale bend into the right knee, being mindful the knee is over the middle toe. It may not be in your body just yet to bring your hands together over your head, so its ok if your arms are apart. Give yourself a break, there is a lot going on in this pose.

make sure too that you are breathing full even breaths. in time you will master this pose, thats why yoga is a practice.....good luck! I hope this helped some.
namaste~
Tracie