Could someone tell me what I have done wrong to this assembly?

Since you mentioned attaching your assembly and the layout for the exploded view, but I can't see attachments, I'll guide you based on common issues in creating exploded views in CAD software (like SOLIDWORKS, Onshape, or Fusion, commonly used for such tasks) and the requirements you described. The issue seems to be that your assembly is complete, but you're struggling to create an exploded view that matches your homework requirements or to collapse it for a drawing. Here’s a concise troubleshooting guide:
Common Issues and Fixes for Exploded Views
Incorrect Explode Steps:
Problem: Parts may not be positioned correctly in the exploded view, or the sequence doesn't match the required layout.

Fix:
In SOLIDWORKS: Go to the Assembly toolbar, click "Exploded View," select parts, and drag the triad manipulator along the correct axis (X, Y, or Z). Create multiple explode steps for each component or group, ensuring the distances and directions align with your layout.

In Onshape: Open the Exploded Views panel, click "Add exploded view," select parts, and use the triad manipulator to position them. Adjust steps in the panel to match the required layout.

In Fusion: Switch to the Animation Environment, use the Move command to manually explode parts, and adjust positions to match your layout.

Check your homework layout for specific distances, angles, or part groupings and replicate them precisely.

Exploded View Not Saved or Linked to Configuration:
Problem: The exploded view may not be saved with the correct assembly configuration, causing it to disappear or not appear in drawings.

Fix:
In SOLIDWORKS: Ensure the exploded view is saved under the correct configuration in the ConfigurationManager. Right-click the exploded view and select "Edit Feature" to adjust if needed.

In Onshape: Verify the exploded view is saved in the Exploded Views panel and linked.