There are a few reasons why your scones may not have risen. Check your baking powder. For maximum efficacy, the baking powder should be used within six months of opening. To test your baking powder, drop a small amount into hot water. Look for bubbles and fizzing. If a reaction occurs it's still good to use. Kneading the dough for too long will make them tough, dense, and shorter. Using too much flour will make the dough too stiff to rise to its full potential. I recommend using a kitchen scale to measure your ingredients by weight rather than volume. Accuracy matters particularly when baking.