Selfish?

On Father's Day, I'll be one day away from being 28 weeks. My in laws really like going to eat Vietnamese food and shop at the Vietnamese markets that's more than an hour drive from where we all live. They're already talking about going down there for Father's Day. Whenever we go there, it's literally an all day affair. My husband does all the driving; we have to pick up my MIL then then my FIL and his two aunts. One of his aunts lives near my in laws, the other does not. She lives about 20-25 minutes away from them. When we come back, we drop her off first, then his aunt and finally my parents in law. We usually leave around 12 and don't get home till 9 pm, the lastest was 10. Being pregnant, I really don't like sitting in the car for that long not to mention it gets hot out there. Would it be selfish/disrespectful if I didn't go with them on Father's Day?