You don't need your undergrad results in order to apply for a Masters. You can get a Conditional Masters offer in the same way that you do for an undergrad degree.
For example, I applied for my Masters in the November of my third year undergrad. I was given a conditional offer of a 2:1 or above and two good academic references. Both of my references were in by the first week of January. When my transcript was sent to me the following summer, I submitted a scan of this and my place became Unconditional (different unis want it submitted in different ways). I then had to produce the original transcript in order to enrol at the start of my Masters in September.
Each uni hs a different Masters application process, so I can't say whether your target uni will want to know your detailed marks so far on your application. All I can tell you is that mine didn't. You also need to bear in mind that your referees may choose to comment on your performance and unit/module results. You might want to choose referees with whom you can talk this over in advance, so that you can understand what they plan to mention.
Most universities will need to see your full official transcript at some point, as your degree certificate will generally not be available until your Masters course has started. However, the Masters offer will be based entirely on your final degree mark.If your transcript shows that you got the bulk of that mark by slogging in the third year after slacking in the second year, then aced the dissertation, this will mak no difference. If you get the final result on your Conditional offer, then you will gt the place.
You can always use your application to spin poor unit results if they're relevant to the Masters course and might be a problem. e.g. "Whilst I struggled with xxx in the second year, I enjoyed it and my marks were much improved in the third year".