Its my SiL's (SiL2) 40th on Saturday. My eldest SiL (SiL1) is hosting an evening meal at her house for SiL2 (they are sisters). Ages ago, I emailed SiL1 to ask if there was any way DP and I could contribute to the food/preparation to lighten her load. She gratefully replied asking if it would be ok if I made the birthday cake, which we could have as pudding. Great - I love baking birthday cakes so enthusiastically agreed and have spent a small fortune on ingredients and taken Friday afternoon off work to bake it.
I've just had an email from SiL3 (SiL through marriage - not a sister) saying that she is making the pudding for SiL 2's party, and asking my opinion on her choice of dish. I assume SiL3 has just asked SiL1 how she could contribute, and SiL1, not being particularly organised, has either forgotten I was making a cake, or has run out of tasks to hand out to willing helpers and thought it wouldn't hurt to double up on desert options, and told SiL3 to liaise with me over pudding.
Rather than get all angsty about my toes having been trodden on, I replied with positive encouragement at SiL3's choices of dish and added that SiL1 had asked me to bake the birthday cake, and perhaps we could have the cake with coffee or take slices away in doggy bags. I copied in SiL1. There was not a hint of subtext in my email.
I'm really trying to rise about any potential pettiness here, but I can't help but anticipate a bit of catsbumface on my part when everyone politely declines a slice of lovingly prepared birthday cake as they are so stuffed from SiL3's pudding. I'm outletting on MN at having to be adult IRL when really I want to stamp my foot and scowl that I'M supposed to be making the effing pudding 
AIBU to have a little catsbum to myself at the inevitable rejection of my cake? Or have I handled this all wrong? Preying LeQueen drops by to help me have a word with myself