Hi! dont't worry so much about it. your baby still have a lot of time to turn head down n engaged. Babies will usually engaged when they are ready to be born. To prevent heartburn try not to eat spicy food n do not eat before you sleep. Try to have your last meal at least 2 hours before sleep. As for ribs pain it cld be your baby's legs kicking or hands pushing.
your gynae will be able to tell whether your baby is head down or head up just by feeling your tummy. They dont't have to scan since your baby is big enuff to be felt by hands at 34 weeks or so. Trust me I know cuz I gave birth at 34 weeks even though thru c-sect cuz of complications. Was hospitalised for a week before giving birth n everyday my gynae will come n feel my tummy to know what position baby was in.
So dont't worry so much alrite. just take good care of your health, eat healthily n rest well too.