I'm so happy to hear that you're interested in engineering! You were correct that you need to take Calculus 1, 2, and 3, linear algebra, differential equations, and possibly some additional math credits depending on the program. As you probably already know, math is a subject where each course tends to build on the previous information. My best recommendation would be to take as much math as you can in high school - especially AP Calculus if your high school offers it. Make an effort to make sure you really understand what you are doing and why you are doing it. Outside of math, I think it'd be extremely helpful for you to take a physics class or do some reading on your own time about the basics of physics.
As far as which major is easier - it really depends on the person. Mechanical engineering is easier for some because it is in the physical world - you can see how things work together, whereas electrical engineering is a bit more "imaginary" since we cannot see electricity. When you're deciding on where to go to college, I'd make sure they offer both a mechanical and electrical engineering program since you aren't sure which you'd like to study. After you've found the colleges you're interested in, you can look into the different rankings to help you narrow things down. There are a lot of factors in choosing a college, so make sure you weigh all your options!
My last piece of advice is for you to consider a FIRST robotics team if your school has one. If it doesn't check out the FIRST robotics website as there are a lot of good local opportunities. Best of luck to you with whatever you choose to do!