You'll be fine to pass this hair test. THC stops depositing into the hair 2-3 days after your last smoking session. From there out you will be growing only clean hair. You said that you had several haircuts since your smoking session, thus removing some of the dirty hair. I would continue on with your plan and get another trim before test time. Just make sure that you have at least 3\4 of an inch of hair for the collector. Otherwise, they will take it from another region of your body.