The last line of the ode tells you that the bolded words make more sense when you add the letters "WE" to them.

When you add "WE" to the bolded words, you get:

- SWELL
- FAREWELL
- JEWELRY
- UNFOLLOWED
- GUFFAWED
- WEEKS

The (10 11) in the title of the ode tells you that the "WE" is the tenth and eleventh letters of FORESHADOWED.

Each bolded word corresponds to one of the number pairs underneath the ode. The number after that pair tells you which letter from the bolded word is important.

By matching the bolded words and the pairs, you get:

(8 9) = fourth letter of UNFOLLOWED
(5 6) = first letter of FAREWELL
(6 7) = third letter of GUFFAWED
(1 2) = fourth letter of WEEKS
(2 3) = third letter of SWELL
(3 4) = seventh letter of JEWELRY

and you can string those letters together to get the final answer OFF-KEY.