Similar experiences of having to ask for a Dissertation resubmission?

Hello, I've royally screwed myself this summer in relation to my MSc Dissertation, I've done nothing but stress about it all summer and took me until 3 weeks before the deadline to officially start it, it's now one week to go and although I can see what has to be done, although I am sure its too much to do in the time remaining.

I'm stuck between being mentally ready to just finish my masters but also do not want just a diploma next to my name after how stressful the year has been, I'm tempted to ask for an extension but doubt I'll get it without extenuating circumstances on paper (I've struggled mentally all summer but got told by university doctors they didn't have the resources available where I was to get help for it, I've now got an appointment back home but feel it will be too little too late for my university to grant an extension). Or can I ask for a resubmission so that I can actually get the work to its full potential now that I can see what needs to be done, Once again doubtful it will get granted, but there's nothing worse than knowing your whole summer was wasted stressing and you may only get a diploma instead of the needed MSc.
sorry for ranting just a lot I needed to get of chest