Phew! You've done a lot of work but it's all over the place.
In your order form you have no link between the detailed lines and the invoice, so it's returning all lines in the table. You can't see that because the subform is badly designed. You've calculated the line total in the query, [atotal] yet you haven't put that field on the form. If you use that field, and change your total in the form footer to =Sum([atotal] you get the total, but it's not the total you want!
You need two tables for your invoices, one for the invoice header and one for the invoice lines. You seem to have four tables. The invoice form (your order form) needs to be based on a query that links those tables. Put the header details in the form header and the lines in the form details, not the form/subform setup you have now.
Other problems? Your object names are full of embedded spaces, you should adopt a naminmg convention like tblCustomer, qrySales, frmOrder, etc. You appear to be storing the stock on hand quantity in the product table. This will cause errors if you try and create two transactions at the same time or you start one and abandond it. The stock balance will be wrong.