These ears are by no means incorrect or bad, however they have that distinct "from imagination" look. The structures are all there, but their shape is approximate and especially their proportions look a bit incorrect.
I recommend you try a few more ears, but with photo references on the side, which combined with your anatomical knowledge will result in perfect-looking results! This approach may also help you achieve slightly more natural looking shading/rendering.
Keep at it, and good work so far!