Your two previous courses focused on computer programming. C++ is a language. It has a bunch of syntax you learn to use. They also had a mild introduction to computer science. You came across loops, flow control, and your basic large contiguous container (arrays).
Computer science concepts aren't tied down to a language. Loops for example, aren't something specific to C++. Because it is such a fundamental construct, every real (Turing complete) language implements it in some manner. C++ has while and for loops. Python, for example has no direct equivalent to C++'s for loop. But it has a foreach loop, that allows iteration over a sequence. The same computer science concept is expressed differently in Python. But it is the same, language independent concept.
Data structures and algorithms will be your first real computer science course. Yes, C++ may be used. Or maybe another C like language. But you won't be focusing on C++. You'll be focusing on CS concepts. DS&A also happens to be a fundamental course, and a foundation course. You can simplistically describe an approach to CS problems as: figure out data structures needed, and then the algorithms to operate on those data structures. You cannot proceed without going through DS&A.
Your past two courses focused on getting C++ syntax right. So none of your problem sets/homework assignments really tested your ability to solve arbitrary problems and to be able to visualize an implementation for it. This is a second turning point for most aspiring computer science students. If you don't like programming itself, well that's that. But you also have to be able to visualize a solution to an arbitrary problem. It won't be, okay here's a problem, let's look up a similar problem in the textbook and reuse the code. You're given a number of concepts (data structures and algorithms), and you need to put them together arbitrarily to solve your problem at hand. For some people, this is straightforward, and for some people, it's pretty much impossible. They get the programming syntax. They understand the concept of a certain structure. They just can't put 2 and 2 together.
That's why, you should take this course early on. You'll know for certain if you like computer science. You'll also have the critical foundation necessary for other CS courses.
Because this is primarily a critical thinking course, try to find either classmates who you know for sure are able to handle the concepts easily and breeze through the course, or work with your TAs and professors.
It would be really bad if your C++ is shaky. Or whatever language is used in DS&A course. If it's C++, get a good C++ book. C++ Primer (4th Edition) by Lippman is golden. Accelerated C++ by Koenig is another quality book, but it's more like a book you learn from than a reference book. There's other advanced C++ books to have, but you don't really need them for the DS&A course.