小学生のときに夏休みのプールの特訓でずっと泳ぎの練習したけど、一度も泳げたことがない

sinceは小学生のときの場所に使えばいいのでしょうか？
一度も泳げたことがないは、
i have never swimed in my life　でしょうか？
この時はin my life よりonce が適切でしょうか？
長い分で混乱してます。
私の文の英訳手伝って下さい。

Even though I was trained specially in swiming throughout summer vacation in elementary school, I’ve never been able to swim. 　

I practised swimming a lot during the summer when I was in elementary school but I’ve never been able to swim
かな？
ちょっと自信無い 　

Even when I was a elementary school student,I practised to swim very hard ,I still couldn’t swim well.

ごめんなさい、トピ主さんは今も泳げないのですか？それとも小学生だったときのみ泳げなかったんですか？

　

I practiced a lot in summer swimming school when I was an elementary school student, but it didn’t work.
どうでしょう？ 　

I used to swim alot when I was in elementry school, but since then I have gain about 80 pounds and can’t swim to save my life! 　

I took a swimming lesson during the summer break when I was in an elementary school, but I never was able to swim even once since.

このsinceは今でも泳げなかったら付けて、今泳げるのならonceで終わる。 　

If you are going to teach or correct someone for that matter, please do it right!

I took (NO a) swimming lessons during the summer break when I was in (NO an) elementry school, but I still can swim. 　

look who’s talking?

>I used to swim alot when I was in elementry school, but since then I have gain about 80 pounds and can’t swim to save my life!

alot -> a lot
since then I -> since then, I
have gain -> have gained

>I took (NO a) swimming lessons during the summer break when I was in (NO an) elementry school, but I still can swim.

I still can swim -> I still can’t swim 　

nobody gained 80 pounds or took more than 2 swimming lessons.
only "an" before elementry school was unnecessary. 　

I was merely pointing out res5’s mistakes.
The 80lb. thing was his/her idea of a joke.
But, as you can see from "ずっと", とぴ主 obviously took many lessons in a long period of time.