Yes and No.
You can race in races that do not filter ZP riders.
You can continue to race and have lots of fun just as you are.
The only site that will filter you is Zwift power.
Zwift will still allow you to enter any race but you wont get the points and the rankings but every thing else is the same.
You should really go over your set up.
there are things that can make your power artificially high.
wheel slip. Make sure your tire pressure is 100 psi and the wheel is tight against the roller.
Make sure your wt and Ht are correct. LBS vs KG.
If your trainer has an adjustable resistance, make sure it is set on the proper setting.
This can be tricky. My trainer is supposed to be set on #3. My first year, my power was also mid to upper B. i’m not really that dominant in real life.
I found that there was slack in my cable adjustment and the first “click” was not increasing my resistance. It was just taking up the slack so actually I was riding at level 2 instead of 3.
Try to borrow another trainer from a friend or bike shop and repeat a FTP test and ensure the results are the same.
Level B is really hard and most people don’t accidentally find themselves a level B.
Finally, if you really are that strong but don’t want to buy a new trainer, increase the resistance to bring you FTP down to 2.8 - 3.0.
You will be handicapping your self but you still get to race as a cat C and be very competitive and you will get stronger and you will not get DQ’d.
Most racers will object if you give yourself an advantage but nobody seems to care if you handicap yourself even if the inaccuracy is of the same magnitude.
Just ignore Zwift Power. Over half the racers in any given race are not registered with the site anyway. I like zwift Power a lot and I try to encourage people to register but having a Zwift Power account is not required.
Over all, I can’t emphasize enough, make sure your power is really that high. That is very very strong.