Thanks for your response Steve. Agreed, a big move in the market should not have made a big difference in the P&L. I underestimated the dangers of using stop orders and it's potential for such bad fills. If anything good comes from this, hopefully someone else is reading this post and learns from my mistake!
I've actually been contemplating buying your course for a while. I may take you up on it. Although I feel like I have an understanding of butterflies, there's probably a lot more I could learn.