Turn on your back.
The Indonesian-English pair doesn’t match, according to an Indonesian native speaker and a Malay speaker who is also fluent in Indonesian.
“Angkat kepalamu” means “Raise your head!” – A typical situation for this sentence is like this: You are so sleepy that you are diving your head into a desk during a class, and your teacher tells you “Wake up!”
Here are alternative translations proposed by responders on HiNative:
Balik badan! = (lit.) Turn your body!
Berbalik punggung!" – Note: “berbalik” is interchangeable with “membalikkan” and “berpaling”.