I Need to Know How to Use the Opalescence for my Teeth Whitening Trays?

About 6 years ago I had major dental work done from a great Cosmetic Dentist. I spent over $12,000. I haven't used the trays in 3 years or so. I went and picked up the Opalescence started using it today. It's different from what I used before. It's so thick it's hard for me to judge how much to put in my trays. It's hard to believe I used that much. What am I doing wrong? Can't afford it if it goes this quick. Thanks