First of all, if you're growing 100% organic, there's no need to flush. You just keep watering until you think it's ready then you chop it once the soil is dried out. If you're using bottled nutes and require a flush, sure get a scope to check trichs, but since you're at your first grow rule of thumb is when you think it's ready, leave it another two weeks. We all get eager to chop down our first plant and most of us chopped it too early out of excitement. Keep feeding it until you see the symptoms that it's nearing the end, orange pistils, yellowing leaves, etc. Check the trichomes, if they're still clear, keep going until you see them get cloudy, and then when they begin to amber, start the flush. Don't stress too much about it, you'll get the hang of it in no time.