37 weeks and scared...?

At 35 weeks the doctors measured me and instead of about 34/35cm fundal height i was 29cm... had a scan and baby was showing at 4 pounds.. im so concerned.. i have another growth scan on thursday and if baby hasnt put on weight i will be induced.. i dont really think i have gotten bigger and babys are soposed to put on half a pound a week arent they? im wondering if anyone else has been in this situation. thanks x