Hi Girly Girl
First I would expect your placenta to move away from your cervix long before you are due to give birth.
Your back is a little stronger than some people however it can be damaged by doing things like poor lifting. This problem is caused by a hormone called relaxin. This hormone causes all your joints to become loose in preparation.
You do not say how high your Blood pressure was but I bet that taking your BP was one of the first things that they did. It is common for your BP to go up when you are excited, anxious or scared as you often are when you go for a check up.
The reason that you are measuring 27 weeks instead of 24 is probably due to the position of your baby and is nothing to worry about. In fact most places no longer measure the height of your fundus because it does not accurately tell you anything significant.