Husbands Step Mothers Husbands Bday

My SMIL is throwing her husband a bday potluck, and she invited my husband and I. I, however, don't want to go the driving being around 3 hrs away . And when we get there, baby labor will be on me, and I know half the people would want to touch and hold my 7 month old. (Ewwww) Also, it being a potluck, I'd have to make something for the party. I'm the better cook between hubby and I. So almost 3 hrs drive . Then I got to stress if baby is sleeping or not . Pack food for baby , travel bassinet, and then stay there for a few hours and then drive back home. The mental load is already too much, and it's not even the 7th yet. I'm not sure how to tell my husband I don't want to go.