I had the same feelings. One way or another this evaluation process is going to give the doctors and you a more thorough understanding of the specific issues you are facing. There will be answers even if it's not adhd.
By your description it sounds like a slam dunk. But you are doing the responsible thing by hedging your bets, not counting on it being adhd, and the way you feel and have carried on by side lining hobbies and social events to further your success (effective or not) is good because it also indicates that you ARE willing to put in the effort and make appropriate sacrifices. My psychiatrist wound up diagnosing me with ADHD and issuing me medication for it, while also indicating a possible personality disorder. In the moment I was hesitant about that suggestion, but I am not ruling it out now with treatment. I am so significantly improved it isn't even funny, but there is a lot of self worth issues to work through, and my treatment and ongoing treatment is by no means going to be a single thrust.
Also it's just adhd, and classed primary inattentive or primary hyperactive, or combined type. The hyperactivity tends to just die down a bit in adulthood and turns into internal restlessness, or be passed off as being energetic. ADD is no longer a DSM diagnosis. It's all going to change probably for the next version of the manual as well as they further refine and research it and find better ways to categorize it. Semantics.
Don't worry about the diagnosis. Do your masters application right now. You are going to be better by the time it gets rolling. You are going to get past these hurdles adhd or not.
And if for some odd reason you are not diagnosed you can always request your files and seek a second opinion : if they don't offer a positive plan of action and something else that seems like it has the potential to be right and help your performance which sounds like the core of your problems.
Again... these feelings if anything kind of indicate you do have adhd, to me. If it was just depression you wouldn't be cancelling things to try to be productive, you would be cancelling them because you felt like shit and didn't want to be a burden or were overcome with anxiety or fear or whatever.
No worries on the long post, it's best to even just break it into paragraphs once in a while even if it isn't structurally correct, for the sake of us all having adhd and all. I totally get the stream of consciousness though.
Seriously though : you are most likely adhd. Stop worrying, and do the future medicated (I assume) you and get that application filled out and submitted. You are going to DESTROY your masters with your work ethic, seriously. You'll make up for any ''lost time'' and frankly, knowing isn't doing. You probably KNOW all then things you should know from your education, you just had trouble applying and demonstrating them. Adhd is a bit of a gift in other ways sometimes, you will be a great employee. We are fantastic and pulling together disparate sources of information, drawing links between related things that others often miss, and have tremendous creative and logical talents (some lean one way or another but I think most wind up fairly gifted one way or another.)
You will need to do some therapy at some point to work through your self value issues, they will still be a barrier to your success, although focusing your effort on generating that success will effect it, don't forget to work through old things with some help later. And cognitive behavioral therapy is very important for adhd once you reach adulthood. Gotta flex those muscles you never have or gave up trying to use at age appropriate times, CBT teaches you what they are, like cognitively interrogating your emotions, evaluating them, modifying them.
You are going to be okay. Masters application. Now. :)