Take another look at the sentence:
Christine sprang out of the bed and saw bright sunlight streaming through the windows. She knew that Dr. Armour would not tolerate another late, so Christine leapt back under the covers and sleapt until noon.
The third verb, sleapt, is the problem. The sentence requires the simple past. Slept is the correctly spelled form.
|Verb||Simple Present||Simple Past||Past Participle|
Leapt, the verb you chose, is perfectly correct. Before you continue, review the rules for irregular verbs.