There's some stress in trying to decide which category to ride in (and therefore which race). Keep in mind that cyclocross is a short intense race, not a long, slow endurance event.
The cyclocross committee is trying to be flexible for the first couple of events with the B and C races and where there is doubt (and sometimes even when there isn't) allowing riders to pick the B race to start the season. We will, however, make changes by the 3rd race.
If you were lapped 2 or 3 times at St. Adolphe we strongly recommend that you move to cat 4. The experience will be much better. As your skills improve to beyond the cat 4 level you can be moved back to cat 3 again.
Here is a link to category FAQs that is a little easier to read than the post below.