Take a look at the passage again:
To make her ex-boyfriend Brad jealous, Georgia saved her money. To buy a
head-turning black dress that would attract a flock of men at the dance.
You chose to attach the infinitive phrase to the main clause in front, like this:
To make her ex-boyfriend Brad jealous, Georgia saved her
money; to buy a head-turning black dress
that would attract a flock of men at the dance.
Unfortunately, you cannot connect these two parts with a semicolon. Review the rules.
Go back to the sentence to try again.