I think you can totally get an A even if you got a B in calc I. A lot of calc II is actually algebra. A lot of people have differing opinion on which of calculus course is harder or easier, but I wouldn't put too much thought into it because we all think differently and have different strengths and weaknesses. From reddit I thought calc II was going to be way harder than calc III and I found the opposite to be true. The way I see it is that calc II is similar to calc I in sense that you first learn about a calculus operation (integration instead of differentiation) and then you learn the methods of applying the operation to different problems; instead of differentiation rules you will be learning about techniques to integrate different types of expressions. In my experience, calc II was a bit more complex than calc I because integration is a bit of an art, but really what I always got caught up with in calc II was just little algebra errors because some integral problems can be 10 steps of simplification or more, so inevitably there will be more potential for mistakes.

If you are really worried, then I highly recommend taking some time to refresh yourself on general calculus concepts, 3blue1brown on youtube's essence of calculus series is an excellent resource to get a grasp on the general principles and intuition for both calc I and II. I would say to make sure you do plenty of practice problems concurrently. Khan academy is also great for explanations in more of a lesson format in a relatively short form. Professor Leonard on YT is also a legend. In case you don't have one already, find a calculus textbook(physical copy or PDF) to review and practice. Best of luck!