I've got a bunch of credit cards and just financed a car and my rating went up. Go figure.
The ratings are complicated on their own but as far as any lender is concerned they don't mean all that much. Like, if I was going to go in to apply for a mortgage or new Line of Credit they'd definitely pull my rating to take a look but they'd weigh the rating a lot lower than other factors (income, equity, TYPE of debt I carry, etc).
What you mention is part of the reason why - you can make sudden movements to raise or lower your rating drastically in a short amount of time, which isn't a great indication of your financial status or reliability. Hence, the credit report itself is much much more valuable than the actual rating.
Note, in Canada you're entitled to one free check of your credit report a year to make sure that there aren't any errors on it. This won't give you the rating, but will give you the report.
Also of note, Pug, is that I've never run into a credit check for a job or when renting in Canada. I know it's more common down south and might be spreading here but I've still never run into it.
I wouldn't stress about yours too much, just use the credit card and pay the bill. In your case, time will be the biggest factor in your credit improving.