Formula not adding correctly?

Because D11 and E11 are not EXACTLY what they appear to be
You have them formatted to show only 2 decimals, but they actually contain more than 2 decimal values.
The formula in F11 (or any formula) doesn't care how your cells are formatted, they only see the actual values contained in the cells.

See here with those cells formatted to show more decimals.
EFSnappyfish.xlsx

To resolve, apply the round function to the formulas in D11 and E11
D11: =ROUND(SUM($E$6)+($E$7*K11),2)
E11: =ROUND(SUM($E$5)+(K11*$E$4),2)