Bests & Worsts Reviews from Amazon

I struggled with how to review this product, and I'll explain why. I was given three options when I began whitening my teeth from my dentist. All I remembered was the brand (Opalescence) and that I chose the highest percentage option. Fast forward to a year later, I don't remember the specific percentage, but knowing it was the highest, I found 35% on this site being the highest available. So I proceed with the order of this product. Within 2-3 seconds of putting this on, my gums are burning like WHOA!. I'm pretty tough, but I didn't' last with this in my trays for more than 30 seconds. The photo is of my teeth right after removing the trays. The gums were inflamed, white, and appeared to have separation from my teeth. The result was worse than you can see in the photo. They went back to normal within 30 minutes or so. All that being said, I called my dentist, and turns out they don't offer the 35% version, so the 'highest' version I chose was only 20% (which never has caused this), because that was the highest they offer. The product is described accurately, and I don't feel giving less than a 4-star review is the right thing to do. I bought the wrong product. Just be careful that you're ordering the proper product. This one will burn a lot if you're anything like me.