Panopticlick is looking for things that make you different to other visitors. In this case, fewer people use canvas blockers than don't, so you become more unique if you use one. However, this only means that it is easier to tell you apart from another user - not that they can tell who you are.
Think of it being like a security camera which can only see heights of people passing by (maybe shadows). Can say "tall person went past", but not "Celeritas, who is tall, went past". The Panopticlick increase means that they can suggest with greater confidence that this specific person visited - you've put a box on your head, so now the security camera can see a square shadow. You're the only square shadow, so someone looking at it can say "aha, the tall person with the square head went past" - they are a lot less common than just tall people!
As a result, in order to minimise this kind of tracking, you should try to blend in - no canvas blocking, default settings on your browser, no unusual fonts installed on your computer, always running in a common resolution.
This isn't the same as preventing specific tracking - it only works if no-one is specifically looking for your traces. If you're the only person in a region who visits a specific site, they can fingerprint you easily, even if you blend in perfectly with other visitors by more easily controllable factors. Essentially, it comes down to what you want privacy from:
- Ad networks: block their cookies and adverts, never click on any unblocked adverts, avoid Google
- People you share an office or computer with: incognito mode. It makes you more unique, but protects against local investigation to some extent
- Law enforcement: anonymous VPNs, TOR. Both increase your uniqueness, but reduce the ease of tracking a specific request