So angry!

Okay everyone will probably laugh at me because of how angry I get over nothing but here goes. I have had to share things my entire life and have people ruin my things. Well I just got a brand new car with leather seats and my husbands mom asks if I can take her to the store with her step grandkid. He rides in a car seat so I'd have to put his car seat in my backseat and take them to the store. I'm just worried the car seat will mess up my leather. I didn't want to say yes when she asked but my husband was there and said yes I'd do it. I should've said yes but I am too immature and I hate having to do this. I know For a fact if we had a kid I wouldn't mind putting the car seat in the back bc it's my kid. Will it be mean saying its a rule not to have food in my car I will allow water as that doesn't ruin anything. I know I am being stupid but I can't help it. I just hate having to share when I have done it all of my life and had people disrespect my property.