Here is the original item:
As all of her classmates were sharing
results (A)
Melody quietly left the room
(B) and found
a quiet corner in the hallway
(C) so that
she could see her grade without embarrassing herself in front of her friends.
You wanted to do this:
As all of her classmates were sharing results Melody quietly left the room
and found a quiet corner in the hallway. So that
she could see her grade without embarrassing herself in front of her friends.
A period after hallway makes a fragment. So that she could see her grade ... is a subordinate clause, which cannot stand alone as a complete sentence.
You might want to review the rules.