Double tap with TWO fingers to zoom is correct, and not an inconvenience. I love that the two finger pinch gesture changes brush size and density. As an artist this is more useful to me personally than the zoom, but to each their own. Take a chance, its a great art app especially for getting a concept down professionally and quickly. Also if you hold down it offers copy as well the pleasantly surprising export, which quickly exports the top layer to the photo roll. Previous commenter encouraged my choice of taking chance, I thank them.
Rswholike2draw about Asketch, v2.3.4