My fx-115 es wont allow any decimals, and the word 'dec' appears on the screen at all times

To convert a single result to decimal, press the S<=>D button just above the DEL button. To have all results come out in decimal, press SHIFT MODE 2 to switch to the LineIO mode.

There must be an error in what you report. You pressed MODE then 4: Base-N and now your calculator is in base-N calculation mode (the DEC, Hex, BIN, OCT) numeration keys are active.
To do statistics you must put the calculator in STATS mode.
Press MODE: You have 6 computational modes to choose from
1: COMP, the general computational mode
2:CMPLX, for calculation s with complex numbers,
3: STAT for statistics,
4: Base-N, binary, octal, decimal, and hexadecimal numeration
5: Equation, solving mode, etc..
For statistics, choose 3:STAT

Set the Input/Output mode to MathIO.
To do so, press [SHIFT][MODE] to open (SetUp), then select [1:MathIO].
When in MathIO you can toggle between the display formats by pressing the [S<>D] key.

You don't need to calculate it. Just press
3 . 0 0 9 x10^x (-) 6
to enter the value.

x10^x is on the bottom row, to the right of the decimal point key.
(-) is on the far left column, above the RCL key.

Press the shift key, then the mode key, then find a menu item called fix. It will display 0~9. The number you choose is the number of decimal places the calculator will display in your answers. On my casio (fx-115 ES) the order to do it is shift->mode->6 then the # of decimal places i want it to go out to.

If the calculator is in the MthIO mode it will always attempt to display the result as a fraction. To convert a single result to decimal, press SD. To have the result always come out in decimal (according to the selected display mode), press SHIFT MODE 2 to select the LineIO mode.

To convert a single result to decimal, press SD. To have all results come out in decimal, press SHIFT MODE 2 to select the LineIO mode.

Press the SD key (just above DEL). You may have to press it twice if the first press produces a fraction.

To convert a single value to/from fractions, press the S<>D key.

To get all answers in decimal form, press SHIFT [MODE] 2 to select LineIO mode.

Press the S<>D key, (located right above "DEL"). This will shift the answer from fraction to decimal. This sounds like a pain but having both functions available can be a big plus.