I think adding sulphuric before the oxidizer is a mistake, because the alcoholic function of ephedrine is not inert in a strong acidic medium.
The precursor, then, should be as pure as possible. You can have the evidence of its purity watching the cristallization shapes at the bottom of your beaker when you do the final evaporation. These cristal shapes are very typical.
The oxidation must be performed "at room temperature". Now, in the hot subtropical summer, I put the flask with the dichromate in the fridge the night before. I add sulphuric only AFTER the dichromate and SLOWLY under stirring. When the solution becomes dark and the meniscus is green the reaction is almost complete. If you work properly the reaction doesn't proceed further the formation of the ketone. If you heat it up immediately you'll have the formation of benzoic acid.
You must add the NaOH (or KOH) COLD taken from the fridge only while stirring, little by little, till you see the formation of "milk 'n coffee". At that moment check the pH at every TINY addition of base. When the free base is complete shake in the sep funnel with chloroform, or toluene, or perchloroethylene (3 extractions), then wash it 3 times with distilled water till the free base-solvent layer is light grey, then make the hydrochloride directly in the sep funnel adding first the water with HCl (10-15 drops every expcted gram), after shaking the indicator reads basic. Then you correct to 6-7 adding 4-5 drops of acid, new reading, new corrction, till you reach the right pH. Then concentrate the water till you see the formation of a light greenish cloud. Now filter it and finish the evaporation at moderate temperature. If you have worked properly you'll see the formation of the same typical crystallization pattern of ephedrine, but that is methcathinone, believe me. In the end, add acetone, let it stand a while, remove the acetone carefully with a syringe, then let the last acetone evaporate at room temperature or VERY MODERATE heat. Scrape with a spatula and....have a good day. The powder you'll get in this way is white shiny and the small crystals are needle shaped. Have you ever tried to drink a tea of salvia divinorum while on cat?