The Most Embarrassing Moment of My Life!

My boyfriend’s parents came over for the first time. Everything was perfect—until his mom went to the bathroom.
Fifteen minutes passed. She was still there. Twenty minutes later, my boyfriend checked on her.
When she finally came out, her mood had shifted. She grabbed her bag, and they quickly left. My boyfriend yelled, “You could’ve warned me!”
I went—or more accurately, I rushed over—to see what was going on and suddenly froze when I saw my bathroom in total chaos. The entire floor was covered in napkins, and the smell was unbearable.
That’s when I remembered that my boyfriend’s mother had a severe gluten allergy. I had completely forgotten and had served her a homemade cake that wasn’t gluten-free. They had assumed I would remember her allergy and be careful, and my boyfriend was furious that I had forgotten.
But to be fair, he had only mentioned it once—although he swears it was more than that. Now, I have no idea how to make it up to her, and I’m afraid we’ll never get past this incredibly awkward situation.