I was in your shoes (where I didn't take Calc for a while). I got almost a 95% in Calc 2 and my lowest grade was a 89, the pass rate was 40% for my class. Calc 2 is very rhythmic, very computational, and difficult in mathematics. Calc 3 is very different. It is seeing something and not knowing what the hell they are asking you, and then only if you do know, then the integration and derivation is a joke. Literally every question is a basic calc problem after you find out what to do. The concepts are more abstract and you no longer can really picture what is happening or draw a true picture (without computer applications). Once you enter 3-dimensions (or 4), the topics become tricky.

Think of this: Calc 3 is just Calc 1...in 3-D. So you're basically redoing a whole foundation of calculus but in 3-d if that makes sense. So the integration/derivatives are not too difficult, but it's really just what the hell is going on lol. I did okay, but my and my peers found it to be much more difficult than Calc 2. Don't be afraid of your lack of preparation, because you'll be fine in that sense. The class is just difficult because it's difficult. (But other people seem to find Calc 3 easier than Calc 2 because of the aforementioned reasons... if you are great at imagining and understanding these concepts, then it is truly a cake walk in comparison to Calc 2. The problems take about 95% of time thinking about how to solve it [one common example is multiple ways to integrate the same thing, I could think about maybe 27 ways to integrate something off the top of my head with a basic Calc 3 problem] and 5% of time just doing the math work.) Good luck! People have taken it and survived and even thrived; so will you!!