Hi Bob,
To be honest I don't think that there are many forum members who could eat a sandwich without their blood sugars going high. It has too many carbs. If you really want to still eat bread, (you don't say which type you ate) then try an open sandwich with protein and loads of salad filling and see how that effects your blood sugars. There are members who can eat nimble, soya and linseed or something like that but an ordinary white sandwich loaf has no advantages for diabetics.
Hope this helps,
Catherine.