Basically the OP sounds irresponsible as hell, but he reminds me of myself at the same age so I'm sympathetic
Anyway, you should:
1) do the best you can in the subjects you still have available. Your grades matter, there is no way to get around that. If you have a crappy degree (i.e. a 2:1 from a non elite university, or worse) then you will struggle to get funding unless you do another Masters first.
2) all else being equal, the research parts of your masters count for more than the taught courses (within reason), although both are important. But noone is going to care about an individual research paper that's part of a module, just make sure you do better in your final year thesis (if you do one?). Also references can be important, so try to make sure that the academic you are working with thinks you are good, so they can write you one.
3) if you are smart enough to get high grades at undergrad/masters then you are smart enough to pass a PhD, but there are a lot of factors other than raw intelligence which matter (work ethic, ability to work for months on end on the same boring problem, etc). People dont drop out of PhDs because they are too dumb, they drop out because they are the wrong fit for academic research.
4) you have to be sensible here - if you dont enjoy your masters then its not obvious you would enjoy a PhD. Why commit 3 years to something you dont think you'll like? A PhD isnt going to boost your employment prospects outside of very specific jobs, the main reason to do one is because you enjoy academia.
5) Think long and hard before doing a PhD in biology, or lab science. There are very few jobs, and PhDs are oversupplied. I would recommend doing something that has good industry+academic employment options at PhD level. Personally I done mine in applied maths because I knew that there were high paid private sector jobs I could fall into if I didnt want to stay in academia - I'm not saying you should do the same, but I am saying that you should pick an area where you like the private sector options, because the most likely outcome is that you wont end up working as an academic researcher.