This is an area that has caused many players grief (along with the stuck toads and getting halfway down the chute a little later in the Serpent Temple).
You might also want to try using run & jump keys while squirming around too. Smaller characters have a better chance of getting through. Look slightly up when using the combination of all the keys. Hopefully that will get you unstuck and onto the snake idol!
You've got the responses you need so if you can't manage to get unstuck, at least your game can go on!
Wyv