It is not likely you will get any large heads, but if you want to go for some side shoots, you must cut all flowers off. Then watch it closely for the side shoots in the leaf axils. They will not be large heads, maybe an inch wide or a little more. Pick them before they open up into flowers. Some varieties of broccoli send out loads of side shoots. It may take a little cooling off before they get going good with the side shoot production.
there is no broccoli and there have been a few flowers.
The part of the plant that we pick and eat is the cluster of flower buds. You must have this before you can have flowers. This is why I say, "watch it closely". If it is blooming, you just missed the head when it was ready. Yes, it sounds like it was a small head because of the heat. Good Luck.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-