Because there are so many variables to consider, the rating systems are only an approximation of the inherent ability of the boat. Any given boat might not actually perform up to its rating because the bottom or keel is foul, or because the skipper or crew are unskilled. Likewise, a given boat might perform better than its rating if it has been carefully prepped to race, or if the skipper and crew are more skilled or experienced. Because it is only an approximation, that means there are things that you can do to help it perform better than its rating. That''s where boat preparation comes into play.
In any competition, you should always realistically assess your strong and weak points. Your weak point now is that you are inexperienced. Therefore, you need to find some way to make yourself competitive, until you can accumulate enough skill and knowledge to win by your wits. The best way to gain that edge is by prepping your bottom and keel, because that will enable your boat to go a little faster and point a little higher and perform a little better in every respect. If, relative to your competition, you gain a slight edge in raw boat speed and boat performance, that edge will compensate for some of the mistakes you are bound to make as a novice. If you race actively for a few races, and analyze your major mistakes after each race, and concentrate on avoiding those big mistakes thereafter, your racing results will improve noticably by the end of the season. When you tack or change course, learn to do it smoothly, and to re-trim your sails efficiently, without allowing your boatspeed to decline excessively during a tack. Learn to steer a straight course, without oversteering. Concentrate intensely on sail trim, so that your sails are always perfectly trimmed to your course and to the wind direction and windspeed.
In most club racing, you can win by making fewer mistakes than your opponents. In more competetive racing, your opponents won''t be making very many mistakes, so, you have to use superior racing knowledge and skill to beat them. If they know a lot, you have to know more.
My first cruising boat was an old Catalina 22, which is not particularly noted for its racing ability. I sanded the bottom and swing keel and gave it a fresh coat of hard-finish bottom paint, and won the first race I ever entered. My "strategy" was to keep my boat going as fast as I could all the way around the course, and stay as close to the fastest boats as possible. Yacht racing can be as complex or as simple as you want it to be.
As the others say, just get out there and do it. Yacht racing is not a physical sport. It is cerebral. From your questions, it is obvious that you are thoughtful and eager to learn, and that''s really what it takes to be a good racer.