Develop a loan amortization schedule for a $3,000 loan at 56% interest rate per annum compounded weekly, repayable at the end of every week for 25 weeks. In addition, demonstrate your financial mathematical process by calculating the weekly instalment using the Financial Calculator and Microsoft Excel, clearly show all the steps involved. 

Verify your answer using the appropriate Financial Calculator and the Microsoft Excel Spreadsheet Function to confirm that your manual calculations are accurate. You are required to show the relevant screenshots