You know what? Shame and guilt are the undoing of all of our best intentions. Here's what I suggest: It is a party... a little cake isn't a big deal. Just keep the serving small.
Instead of telling yourself what you "won't eat" and then feeling bad when you can't meet your expectations. Tell yourself what you "will eat".
I will eat 6 oz of chicken.
I will eat quinoa instead of white rice
I will eat 2 eggs for breakfast
I will eat a whole ton of steamed veggies for lunch.
You get the idea. I am guessing that the shame and guilt is causing you a whole lot more anxiety about food than is really warrented. Food is good, not the enemy. We just need to adjust our food selections and portions sizes and then celebrate all the good things about sharing a meal with those we love.