The drawing:
From an engineering design stand point the model has flaws, but that was not the point of the drawing. Everyone has to start somewhere, and this is a great start. I am not too familiar with MD but with ProE and SolidWorks you can perform FEA and stress analysis on the models (assuming you know the material each pikes is made of). After you design a new car, and I have no doubt you will, try and see what happens if you have loads on the car, i.e. turns and loops etc. But enjoy drafting and design because you will probably always have to do that in some aspect of design.
School:
Are you planning on doing Mechanical Engineering or more like manufacturing engineering? If you were going to get into ME I would recommend hitting the math hard and get it all out of the way. It is amazing how it seems like you never use any of that upper level math and then one class you get to solve differential equations.
The most important thing you can do is not get unwilling to push through the hard times. Engineering is hard, and no matter what you will spend so much time working on projects and in teams, it gets tiring.
On a side note, taking business classes really helps out for some reason. I had always thought of the business school as the evil empire.
And another note, learn how to write technically, this will help out, as all employers are looking for good writers. In fact that is probably just as important as being able to speak well.