This is a water-based product, so essential oil will not dissolve in it. Essential oils will only dissolve in water-based products if a solubizer is added. After a little searching, I found that Solubol can be used to disperse essential oils in water. I have also seen polysorbate-20 suggested, but I am finding it suggested for room sprays rather than for application to the skin, and there may be a reason for that.
I would not recommend including essential oils in my recipe without first doing quite a bit of research into skin-safe solubizers. Also, any additions will change the percentage of other ingredients--that is, it would reduce the total percentage of glycolic acid. Any adjustments to the formula would require careful calculation. Remember, too, that some ingredients have maximum usage rates. Making adjustments would require a knowledge of maximum recommended usage rates for specific ingredients.