From what I can understand, you need to figure out how many credits you have at a first and how many are at a 2.i. If the majority are at a 1st, then you might get a first?
At my university they did this, but the other caveat was you needed to have an overall mark of x8%+ (i.e. to go up to a first it needed to be 68%+ and also needed most of your credits in the class above).
Could email whoever deals with this at your university, can't remember who they're called...lol. Either way, you've done really well in your final year!