It's okay, you have until 〜 to learn it＝大丈夫だよ、〜まで習えばいいんだから
It's okayと一言添えるだけで相手も安心するでしょう。
You don't have to know it by heart until〜＝〜まで全部分からなくていいんだよ
know it by heart＝完全に理解する
Good luck!
As long as you are able to read Hiragana by the first grade, you'll be fine.
If you can do your times tables when you're in Grade 3, you'll be fine.
If you stop peeing your bed before you start grade 1, you'll be okay.
この場合、次のような言い方ができますよ。
ーAs long as you are able to read Hiragana by the first grade, you'll be fine.
「一年生までにひらがなが読めれば大丈夫だよ」
ーIf you can do your times tables when you're in Grade 3, you'll be fine.
「3年生で掛け算ができれば大丈夫だよ」
ーIf you stop peeing your bed before you start grade 1, you'll be okay.
「1年生になる前におねしょが治れば大丈夫だよ」
ご参考まで！
アメリカ合衆国 
カナダ 
