Is science or math more important in mechanical engineering?

For mechanical engineering, it's all very basic physics (classical mechanics) that is used to analyse complex situations. It's not the physics concepts that make engineering curricula hard, it's learning how and when to know to make assumptions and which concepts to apply. If you're interested in physics, I would shoot for a degree in physics, nuclear engineering, or electrical, since those fields tend to use more interesting physics regularly. If you like math, I would shoot for a math degree or electrical engineering (lots of EE is applied math--signal processing, communications, controls, and machine intelligence)

I think it depends what subfield of engineering you are interested in. Of course, all three are important for any engineering specialization, but if you want to be a chemical engineer, obviously chemistry will be the most important to you. But to get into a good engineering school, I think you must have good grades in at least maths and physics. I think they consider chemistry less important, unless you're going to chemical engineering. So my advice to you is to work on your physics as hard as you can. Obviously you're smart enough, since you can get an A in maths. If you work hard enough and practice as much as possible, I think you can make it. Try to solve a lot of problems. That helps a lot in the understanding of the material.