I just wanted to note that a lot of product designers *do distort sketches for the purpose of presentation, as well as their own versions of ‘flashiness’ - have you ever seen sketches for the Triax watch? There are plenty of other noteable examples in books. When we sketch electronic products, we make them thinner, the buttons smaller, and the materials higher quality than the actual product will no doubt have. Just consider it next time you’re drawing without an underlay.
When you’re drawing something that small (compared to its actual size) you have to exaggerate it to produce the desired affects. An inch or two on a real car makes a huge difference, so it needs to come across as an even bigger difference on a 10-inch sketch.
In terms of sketching cars - you just have to do it, a lot. People will tell you to practice drawing large, but don’t be afraid to draw lots of small sketches too. They are very efficient and use less paper! You can always blow a sketch up and revise it larger. Do overlays of other people’s sketches (not real cars) to learn how they did it. Be fearless about it, and you’ll figure things out.