Resolved questions
Is there a difference between 지금 and 방금?

지금 now, at the time of speaking
방금 'now' but sometimes can be 'just a minute ago, just before' when combined with '~전'

지금 수업 시작합니다.
Let's start writing now

지금 당신을 만나러 갑니다.
Now, I'm going to meet you.

지금 떠나야 하는데..
I should have moved along now.

방금 만났어.
I've just met her.

방금 수업 시작했어.
The class have just started.

방금 뭐라고 하셨죠?
What did you say a moment ago?

Let's start beginning of tense. In Korean, we don't have any present continuous or perfect tense. We just have three forms of tenses but we assume the time or the situation through the context.
So, if you really want to explain those texts accurately, you should listen more and then you can know the exact time and meaning.
- 언제 했어? 지금 했어요. / 방금 했어요. In these sentences, 지금 and 방금 have the same meaning, I have just done this. (just)
- 뭐하고 있었어? 방금 공부 하고 있었어요.
What are you doing? I am studying now.
-뭐할꺼니? 지금부터 공부해요.
What are you going to do? I am studying from now on.

In Korean, the form looks 'past' but actual meaning is 'present continuous' or sometimes 'present perfect'.
People say '방금 전' meaning 'just before' or 'shout time ago' and that was my 'wrong answer' you think.
지금 also means 'now' but I can mean past sometimes.

The problem is Korean language has totally different tenses from that of English, and we just put simple meaning along the context. I'll show you what Korean-English dictionary says

방금(方今)
right [just] now; just this minute; this very minute;
just [but] a moment ago.

지금(只今)
① 『현재』 the present (time); this time [moment]; now; 『오늘날』 the present day.
② 『지금 막』 just; only [but] just; but [even] now; just now; a moment ago.
③ 『지금 곧』 soon; at once; (just) in a moment; immediately.

금방(今方)
『방금』 just [right] now; 『바로 전에』just) a moment ago; 『곧』 at once; in a moment; 『당장이라도』 every [at any] moment.

지금
(只今)
【一】【명사】 이제. 바로 이때. 시방(時方).

방금
(方今)【명사】【부사】 바로 조금 전이나 후. 금방(今方).
¶ ∼ 일을 마쳤다/ 그 소식을 ∼에야 들었다.

지금 = right now, at this moment
방금 = just now, not long ago