RhoGam shot help!

I am 26 weeks and was told by my doctor to get the RhoGam shot at 28 weeks because I'm A negative. However, my husband is also A negative so there's no way our baby could be born with a positive blood type. My doctor said the shot is just a precaution in case I've unknowingly miscarried a baby with a positive blood type. However, that's impossible because I've only ever been with my husband. Is it worth fighting? Or should I just get the shot? I am 100% sure I don't need it but I don't want to cause a fuss!