Take a look at the item again:
To get on his mother's good side, (A)
Rufus offered to unpack the groceries,
(B) but dropped the carton
of eggs that Mom would later need (C)
to make chocolate-broccoli muffins for the church bake sale.
You wanted to do this:
To get on his mother's good side Rufus offered
to unpack the groceries, but dropped the carton of eggs that Mom would later
need to make chocolate-broccoli muffins for the church bake sale.
The comma after side is correct. To get on his mother's good side is an infinitive phrase. When a phrase of this type introduces a main clause, you need a comma to attach it.
You might want to review the rules.
Go back to the sentence to try again.