Ago and past participle

Hi teachers,

I'm wondering whether the sentence marked in red is grammatically correct or not.
Can the words "long time ago" be used with the past particple?
Or should it change to "long time before"?

And for the word "get this", what does that mean?

hoping to hear your kind comments,
Thanks a lot in advance~!
pb


M: Boy, I was so scared of the water at first and hardly went under water. Fortunately, the Saturday section was smaller, so the instructor was patient with me. I learned water adjustment skills on week one, but I needed both the first and second weeks to get used to the water.

W: I understand. I had the same experience before. Frankly speaking, I had taken the beginning course long time ago, hadn’t finished and retook it this time. So you need an extra week to finish?

M: Well, get this. By the third week, I was comfortable in the water. The instructor taught us front freestyle on week three and back freestyle on week four, but I learned them both on the third week.