Have You Ever Seen Double Rainbows?

An One afternoon in of eight and a half years ago, before the French windows in on the fourth floor of the library, I stood seeing a shower watching the rain from beginning and till its ending.

While As it cleared up, [or "While it was clearing up" "while" 在這裡的意思是 "着"] there appeared double rainbows appeared across the sky.

The lower one was brighter; the upper one,  was lighter. It was the first time that I saw such double rainbows, which were [不可用過去式, 除非現在不是瑞兆了] are considered as symbols of good luck.
I forgotting to pray wish for something. I pondered on the fact know that they would disappear soon. I couldn't bear the sight of their disappearance but went and so I walked away.  [不明你心思, 只猜猜]

Later in life, I saw several times more double rainbows. By now they which just did not impress me too much.

Do you know that in nature, at most 5 rainbows can occur at the same time?  In the lab, up to 200 hundred can be created.  I did not know until I researched on this after correcting your essay.

Have You Ever Seen a Double Rainbow?

An One afternoon, in eight and a half years ago, before outside the French windows in of the library's fourth floor of the library, I stood seeing watching and watched a rain shower beginning and ending start and end.

While it cleared up, there appeared a double rainbows across the sky.
The lower one was brighter; the upper was lighter.

It was the first time that I saw a double rainbows, which were is a symbols of good luck.
Forgetting to pray for something, I pondered on the fact that they it would disappear soon.
I couldn't bear the sight of their disappearance it dissappearing, but it went away nonetheless.
Later, I saw several times more double rainbows*, which, frankly, just did not didn't impress me nearly as much as the first too much. 

*rainbows is plural here since there is more than one double rainbow.

Nice work! Obviously this could be interpreted and edited a hundred different ways.