what baseball position are you planning in you're "in the corn"? this
has nothing to do with 'can of corn' in baseball.

In a broad sense, the phrase "to put one in the corn" means to hit
into the outfield (metaphorically, the "cornfield,") as in this
memoir:

"'Go grab a bat,' he urged me. 'You've been fielding all day. Put one
in the corn.'"

Dreams Fulfilled: A Pilgrimage to Dyersville, Iowa
http://www.stairwell.com/doc/field.html

From this general usage, I speculate that "in the corn" would refer to
a fielder. I can't find anything to back that up, so I am posting this
as a comment rather than an answer.

One of the best reference works on baseball slang is "The New Dickson
Baseball Dictionary." You might want to see whether your local public
library has a copy.