Louie, If I've read correctly, this is a 4-bolt toilet, and as you are facing the toilet you've cracked away part of the flange around the left rear bolt only.
If that's correct, you're probably okay, but as Steve & Bob suggest, I'd still look into replacing it soon; if for no other reason than that any repair or "as is" basis will quickly look bad as the cracked area will be hard to keep clean.
If this was a new toilet, you can buy a new bowl base only & put the existing tank on the new base. This is also possible with an older toilet but you have to be sure the tank-to-bowl bolt pattern matches, and honestly, the cost difference doesn't make it worth the hassle.
Think of it this way; it could have been something much more expensive & you've now got the experience behind you to make the re-installation a breeze!