Flip your page over!
The smart trick is exactly to flip your page over (see your drawing from the back). Using the transparent effect of your paper, pointing it to your window or on a light table, will show us all strange lines not really following the perspective. We will also judge better our proportions and design proposal attitude (is it too aggressive? Is it too round? Is our Center Line well placed?…).
Now that you saw where your perspective problems are you can apply corrections improving your sketch!
Try and enjoy.
If you want you can order my “Car Design Sketching Tips” book on line at LULU