Without doubt this is one of the most beautiful songs sung by Miku.
Since my translation is more literal, it’s less beautiful than yours.
Please just take it for your information

薄紅の時を彩る花びら
ひらひら舞う光の中
僕は笑えたはず
Flower petals coloured the time of light coral
In the light those petals were fluttering
I should have smiled
* Literally, the phrase would be "In the light flower petals that coloured the time of light coral were fluttering I should have smiled" but it seemed to be too long.
I translated 薄紅 as light coral though, there might be a word that fits better.
http://www.colordic.org/colorsample/2279.html鮮やかな日々に
僕らが残した
砂の城は波に溶けて
きっと夢が終わる
The sandcastle we left behind in those bright days
Will melt into the waves
And surely, the dream will end
*I agree with Lygerzero0zero
真っ白な世界で目を覚ませば
伸ばす腕は何もつかめない
見上げた空が近くなるほどに
僕は何を失った?
When I woke up in a white world
My extended fingers could not grasp anything/ I extended my arms but I could not grasp anything
What did I lose every time the sky I looked up at got closer?
透通る波(に)
映る僕らの影は蒼く遠く
Our shadows reflected in the transparent waves were blue and far
ほんの少しだけでもいい
君の支えになりたい
Even just a little
I want to help you
形のないものだけが
時の中で色褪せないまま
Those intangible things are the only
Things that have not/did not weathered in the time
透通る波(に)
何度(砂の城が)消えてしまっても
砂の城を僕は君と(作って)残すだろう
そこに光を集め
Even if so many times the sandcastle disappears into the transparent waves
I will make it with you every time it does/disappears and leave it behind
Gathering lights there
*Probably the subject of the second line 何度消えてしまっても is 砂の城sandcastle. 波waves can be the subject gramatically and would be in the usual case. But I think it’s contextually 砂の城 since this phrase seems to make an antithesis of "The sandcastle we left behind in those bright days will melt into the waves" and 透通る波 is not used as a subject in the preceding phrase.
遠く離れた君のもとへ
この光が空を越えて羽ばたいてゆく
そんな歌を届けたい
To the distant place where you are/To you who are far distant from me
Those lights will fly across the sky
I want to send you the songs of the sort[kind]/like them
僕が贈るものは全て
形のないものだけど
君の心の片隅で
輝く星になりたい
Even though everything I (will) give you
Is intangible
I want to become a star that shines
Somewhere in your heart