You have the wrong formula. Here is the correct one:
C = ((1.313454 - (0.132674*F) + (0.00205779 * F^2) - (0.000002627634 * F^2)))
Where F = Temperature in degrees Fahrenheit.
C = Correction
CG = C + (SG * 0.001)
CG = Specific Gravity corrected for temperature
C = Correction from above forumla
SG = Specific Gravity before temperature correction.
Here it is for everone using Degrees Centigrade:
C = ((1.313454 - (0.132674 * ((C * 1.8) + 32)) + (0.00205779 * (((C * 1.8) + 32))^2)) - (0.111112627634 * (((C * 1.8) + 32))^3)))
Then continue with the formula above formula for CG
If you would like to use Excel for this, do the following:
Degrees F calculation
1) Use Cell B3 as your temperature (F) input.
2) Use Cell B5 as your SG input
3) Paste the following into Cell B7:
=1.313454 - (0.132674*B3) +( 0.002057793*(B3^2)) - (0.000002627634*(B3^3))
Paste the following into Cell B9:
Cell B9 will contain your temperature corrected SG
For people using degrees centigrade, change the formula pasted into Cell B7 to the following:
I'm sure that I could have reduced the formula down to something "prettier", but I really didn't feel like wasting time doing that. Besides, isn't that what's so nice about using Excel.
Disclaimer = It is possible that I made a transposition error when transferring this from Excel, so please check the Excel results against a table before using it.