Outsmarting A 3 Year Old

I have a confession to make. I lied to McKayla. She had this horrible habit of picking her nose and eating the boogers. I tired to redirect her to get a tissue. It didn't work. i tried to tell her that a princess does not pick her nose, it didn't work. So I told her that if she picked her boogers, they would turn into spiders. I know, this is a bad lie. However, it did work...well, kind of. She has stopped eating her boogers, but now she picks her nose and wipes it on whatever is available. I promise I try to watch her, so please don't be afraid to come yo mt house. Anyway, last night she was taking a bath and yelled, "There is a booger in the tub!" I asked her how it got there. She explained that she got it out of her nose and then put it in the water. She confidently told me that boogers in water won't turn into spiders. Hoe come she can make up the rules in my lie? I don't think it's fair. Anyway, I am a bad mom for lying to my child, and I didn't stop the problem. Sigh.