We just got our first RV in September - a 31' Class A. Like you, I was worried about driving something so big. The biggest thing I'd even driven was a full-size Chevy van and that had been 30 years ago.
Before I would drive it on the highway, I made my husband drive it to Lowe's late on a Sunday afternoon, just after they closed. I drove around in that big old almost empty parking lot - turning left, right, backing up, everything - until I started to feel comfortable and get familiar with where things are.
You've been given a lot of great advice here. As I was. The videos some have recommended helped me a lot because I kind of knew what to expect before I ever got behind the wheel the first time.
I'm still not as comfortable driving as my husband is, but I make it a point to do some of the driving on each trip and each trip I try to drive more than I did the time before.
For me, the hardest thing at first was to remember to make maneuvers - like lane changes - more slowly. I think in part that's because I'd driven a low-slung sporty car for several years and had to break some bad habits.
As one newbie to another, about the best thing I can tell you is take your time. And don't hesitate to ask for help here. These guys are the best.
Hope you enjoy your new ride as much as we are.