MIL has my car seat

I just need to vent for a second. My MIL has bought our car seat and stroller for us, which was very kind of her and my FIL because it was very expensive. However I am 34 weeks pregnant and she doesn't want to give it to me until the baby shower for her side of the family. This was fine at first as she had planned it for when I was going to be 35 weeks. I was informed last week that she has had to push it back because "something" came up. Now she doesn't want to have the shower until I am 37 weeks pregnant. This stresses me out. I'm a first time mom and I really want to be able to learn all the bells and whistles of the car seat before I bring my baby home in it. It doesn't help that the doctor told me yeasterday I was measuring ahead. I'm hoping everything works out but in the mean time I can't help but be anxious.