Do you have a "MODE" button ?
I just got a TI-30X IIS and it is displaying only three decimal places. I know it has much more precision than this (i.e., it uses pi with over 10 decimal places, but displays pi times two as 6.283).
Other TIs seem to have a format button or something ... this one doesn't, near as I can tell. I may be missing the instructions; a single folded page came with the unit and seems to be more about basic math than "what button does what".