I too had the same problem before being accepted by Emirates. First time i was interviewed was quite a way under the desirable height/weight ratio and so was told to go away and reapply. I did, and after putting on another 5 kilos was accepted...at that point was still 4 kilos under what was required. I would say to you not too worry too much. If you get through the interviews and are accepted, i think that it is highly unlikely that as long as you look medically fit i.e are not anorexic, all will be ok.
Good luck!