Hi Curly Tea, Do I have to use a preservative in my DIY hair conditioner if it’s only for one time use?

I make a hair conditioner out of BTMS and Cetearyl Alcohol (3% total of CreamMaker), distilled water and then use phenoxyethanol SA (1%) as my preservative. I figured out the phenoxyethanol is causing my scalp to be itchy and break out around my forehead. I am wondering if I even have to use a preservative if I only make one batch of the conditioner for one time use? Like if I rinse it (just BtMS, Cetearyl Alcohol, and water) out of my hair after using it or use some of it as a leave in and it dries in my hair... it won’t matter if a preservative is in it, right? Since it dries it my hair mold, yeast and bacteria won’t develop right? Just like it doesn’t matter if flaxseed gel had a preservative if you use it right away and it dries in your hair? Ideally I’d like to just make a conditioner with just BTMS and Cetearyl Alcohol and distilled water once a week to be used immediately after making it. And then I’d have to make a new batch every time I do my hair. Thoughts? If you still recommend a preservative, any suggestions?

Thank you!