Your plan is not too much different from my experience: I took a 3+2 plan and got a BA in physics and math and an BSME, then followed with an MSE a few years later. You'll probably find that some undergrad courses will have to be carried in your master's program to fill in some gaps but these will be in line with your graduate work and should not be difficult. Two suggestions: if you know where you want to go for your graduate work, talk to that school's admissions people before you select your undergrad courses and they should be able to help you choose courses in your undergrad plan to minimize gaps you may have for their grad program. Second, even if you can't cover all these gaps with prior planning, once you get to your grad school look for courses you can test out of or find equivalent courses in your undergrad work. You may have to in initiate the "test out" proposal but you can't lose. The worst they can do is tell you you didn't pass and have to take the course -- which was their plan in the first place.
One other piece of advice: be open to changes in your plan as you get into these areas of study. You may well find that something else challenges you more than automotive or aerospace engineering so don't be afraid to change direction. What you want is a career that is so much fun you look forward to going to work every day, even on Saturdays! Good luck.