Could I have ADHD/ADD (attention deficit disorder) when I was a very good student, looking over my school days?

I suspect myself having/had ADD, but curious if it's possible.

I am 26 year-old South Korean girl who is now a jobless. I was a very good student until I graduated from high school, but failed university because of essay writing. Actually that was also caused from lack of attention, I forgot to write down the finished one from my note to a clean sheet, not knowing that the time is up.

Anyway, there is some cases that makes me fear of having that symptom, such as forgetting of important tasks like job applications or school interviews, accidental loss of quiet big money (approximately 500$, school bus fee).

I am really bad at dealing with all things with dead lines; applications, assignments . . . I was also a bad worker at the previous workplace, since I always made small mistakes like spellings and grammars on reports or official proposals that directly goes to the big boss. I knew those were important and tried by best when checking, but couldn't catch them before my colleagues pointed out. I kept being scolded that I don't fully concentrate on my works.

I felt like there's something missing while I work, just like grabbing sand and feeling them passing through fingers. So I quit work.

Actually I once went to one of the biggest hospitals of my country, and got some tests. Some was paper tests and one was with computer, which made me sit in front of screen and press space bar when certain type of figures (starfish, rectangle etc) show up. Doctor said me that the result shows low score of intention and there also is possible depression and anxiety disorders. He advised me to admitted to the hospital saying that the each drugs for depression and ADHD can be collide so it needs time to check. But at that time I decided not to admitted since I cannot believe his words that I could have ADHD, and also there's one job interview left for a major company I really wished to join. But now, I seriously regret not having admitted to the hospital and get further test/remedies.

Is it possible that a person with a attention deficit problem get a good score in schools? I also find myself afraid of leaving admission record which can make me look like a freak out.

How can I tell this to my parents? I was born as a twin, delivered 3 months earlier than expected with my twin sister. She suffered from retinopathy (bad eyes) till now and my parents still thanked God that I was born without noticeable disorders...

Sorry for my bad English but this makes me depressed nowadays.