Is Calculus hard as a subject?
This sort of question really depends on how much time and practice you put into this branch of mathematics. Calculus can be very daunting to look at at first glance, but like any other language you will need to solidify the foundations first. Once you learn the basics of derivatives and integration the rest seems to fall into place. You will need to learn the notion of a limit and tackle differential equations, but with practice these all become second nature.
As you advance in the subject the basics all stay the same but you will start to learn methods to solve more complex areas. As long as you take care in your working (as it is very easy to slip a sign) the subject is a nice and very rewarding topic. Just practice, practice and practice and you will get there.