I love watching you. I am from Ontario and my mother had a property in Parry Sound. Watching you makes me miss home and feel at home at the same time. (Originally from Toronto - Live in BC now.)
Yup, fragrance oil. Each fragrance oil has a recommendation usage rate and you should always follow that. It takes time to learn which fragrance oils will work with your recipe as well. I made this video a long time ago but if I remember correctly I forgot to add the fragrance oil to one of the layers so the other layers got more - all within the safe usage rate though!