Well, it's past its prime and may be tougher and more pungent than broccoli harvested at the right time. Cut the head off and add it to a stir-fry or something. The plant will send out smaller heads from side shoots.

In case Slimey's answer isn't clear enough - you are supposed to harvest broccoli before it flowers (yellow blooms at the tips). There is no turning back the clock on that one.

When the heads start to loosen up, then they are going to start flowering. If you were waiting for it to get to the size of the ones in the grocery store - it probably won't. The first time I grew broccoli I didn't get a "head" bigger than a child's fist.

Thank u! Good to know, I'll get it and stir fry

You also show signs of having something farmerdill told me last year was called brown bead. Cut out the browned sections there, they don't taste good. (You probably were going to do that, anyway :) )