Here is the item again:
You correctly realized that the comma after ketchup is wrong. To make smiley faces on the burgers ... is an infinitive phrase. When you attach an infinitive phrase to the end of a main clause, you need no punctuation.
To fix the problem, you chose to do this:
You have correctly employed Punctuation Rule 5:
Main Clause + Ø + Infinitive Phrase.
What a brain you have!