Try and get a friend/partner to measure you - even make an appointment with a nurse at your local surgery!
Get your posture right! Even just standing incorrectly can make you lose those vital measurements.
When I was measured a few years ago by a nurse I was just over 5'6" but then the lady at BA who measured me said I was 5'5"! Where on earth did I lose that inch?
If you have an interview with BMED do go, and if you are worried ask them to measure you.