Hi! I Have A Question That Has Been Stressing Me

Hi! I have a question that has been stressing me out. I am now 24 years old and am thought to be approx 5 weeks pregnant. This will be my first child to be born, however when I was 18 I had an induced abortion. I have the rh factor, and was given that rh shot after my abortion, so about 7 years ago. I informed my OBGYN office over the phone when they informed me my blood work confirmed I am about 5 weeks pregnant, and they said that the shot I got 7 years ago is no longer effective and when I am at 28 weeks I will get another shot. I am concerned that in that time frame a miscarriage could occur. Is this something I should be concerned about? Thank you!