By default, the Create [Record] page layout is set to 2 columns. You can customize the page layout and set it to single column by following the steps given below:

1. Log in to CRM with Administrator privileges.
2. Click Setup > Customization > Layouts.
3. Select a Module from the drop-down list.
4. In the Page Layout page, click the Edit icon.
5. In the popup window, do the following:
• Edit the Name, if required.
• Select the One-Column as the Column Layout.
• Click OK.
6. Click Save.
   You can add more sections by clicking on the Create Section button.