Calculate the decision boundary for Quadratic Discriminant Analysis (QDA)

I am trying to find a solution to the decision boundary in QDA. The question was already asked and answered for LDA, and the solution provided by amoeba to compute this using the "standard Gaussian way" worked well. However, I am applying the same technique for a 2 class, 2 feature QDA and am having trouble. Would someone be able to check my work and let me know if this approach is correct? Where $\delta_l$ is the discriminant score for some observation $\mathbf{x}$ belonging to class $l$ which could be 0 or 1 in this 2 class problem.