Did I flush too early?

You probably have another 3 weeks or so to go, so yes, keep feeding for another 10 days and reflush once closer to maturity. No need to do anything weird, just resume nutrients as per normal/what you were doing previously. I find a good indication as to when to consider flushing is when there are about 95% brown pistils, then harvest about 10-14 days later when there are about 98-99% brown pistils (or just a very few white pistils remaining, same thing really!) This will put you in the "10-30% amber trichome zone" without even having to look at the trichomes and is dead easy for those new to cannabis to understand. I have been using the "pistil colour method" for over 30 years and find it easy and reliable. Trichome colour has many variables, such as some plants never getting amber trichomes and others having 70% amber after only 4 weeks of flowering, (which is all related to genetics), that I personally believe basing harvest timing solely on trichome colour alone can be misleading at times and somewhat unreliable.