Don't be discouraged by some of these posts, I went into my ME curriculum behind in math, and was not too fantastic at it either, and still made it through after 5 stressful, fun, tiring, mind enhancing and overall great years. That said, I also proactively pursued internships and jobs because when you have a weakness you have to rely on your stronger skills to counter it. In the end I had a great job of my preference secured at the start of first semester in my final school year and a second offer from my second choice despite a lack luster gpa.
If you want to start your own automotive based design company after getting your ME degree and gaining experience, GO FOR IT! Like most things in life, it's not a question of if you can do it, it's only a matter of how hard your willing to work to do it.
PS: Don't get hung up on the math part, while being proficient at math is important in earning your degree, you won't use it much in most mechanical engineer job duties. Furthermore, their are countless online and school provided resources to help you along the way.