OP, plants can "see" sunlight even when it isn't shining on them. The shade didn't cause the early flower. The length of darkness is what triggers a plant to flower, so running a light for two hours at midnight will trick it into thinking it's summertime. Or you can throw shade to make sure it finishes flowering now. Just cover with a tarp after 12 hours of daylight. Do it every day for a few more weeks and you will a depo pro by the time it finishes.
I'm growing in the bush, so I've just got to ride out my early flower issues.