Read the mock as evidence, not a score
The grade at the top tells you very little. The marked script tells you almost everything. Go through it and separate losses into recall gaps, misread command words, weak application on unfamiliar contexts, and time pressure near the end. A cluster of blank final questions is a timing problem; scattered small losses are usually wording or application.
Fix the causes in the order they cost marks
Rank the categories by how many marks each cost, then address the biggest first. For wording losses, work through the explain-question guide and the command word guides. For recall gaps, relearn the specific topics rather than everything. For timing, practise sections against the clock using the marks-per-minute the paper implies.
Rebuild confidence with tested practice
Confidence returns when fresh, timed work improves, not when notes are reread. Pick your three weakest topics from the mock, relearn each, and answer a question set on it. Then sit a fresh section under timed conditions and compare. The Gap Report helps turn the mock into a ranked topic list.
Keep the mock in perspective
Mocks are meant to be demanding while there is still time to act. Grade boundaries move between a mock and the real series, and revision is usually incomplete when mocks are sat. Treat the result as the most detailed feedback the student will get before the exam, and use it.