Sorry mate, yeah I think they only calculate it on the module results, there's no overall grade that could be bumped up if you're just under the boundary. I know there are plans for the OU to bring in a US-style GPA system so it's clearer if you've got a low first, high 2.1, mid 2.1 etc, though I know it's no help to you right now. No harm in double checking with the OU if you haven't already accepted your 2.1, you never know.