Here are a few suggestions:

(1) I can see making it larger, but you will have to take into account the terrain around the Sarlaac itself - maybe try to make the Sarlaac bigger but keep the sand dunes it is hiding in the same size.

(2) darken and change the color of the overall Sarlaac body in comparison with the sand. Granted, it would try to blend in, but if there was a way to indicate that a much larger creature was hiding underneath the sand as opposed to the sand pit just having a mouth at the bottom would add to believability.

(3) it looks like the tentacles are coming out of the top 2 rows of teeth. If there is a way to make the 3rd and 4th row darker as well as "open and close" ie the real mouth, whereas the upper 2 or 3 layers of teeth are essentially the lips around the mouth, that would explain why there are tentacles there (if it was part of the mouth, granted the tents could be retracted, but wouldn't they get in the way of it trying to eat something?). It would also alleviate the removal of the "audrey beak" if you had the lower area moving and nashing together.

(4) and in any edit, you would have to tone down or get rid of the "rubber bounce" when people land in the mouth.