Let's keep up our friendship even now that we're in junior high school.
I know we're in junior high school now, but I hope we remain good friends like we were in elementary school.
この場合、次のような言い方ができますよ。
ーLet's keep up our friendship even now that we're in junior high school.
「中学でも交友関係を維持しようね」＝「これからも仲良くしようね」
ーI know we're in junior high school now, but I hope we remain good friends like we were in elementary school.
「中学になったけど、小学校の時と同じように良い友達を維持できるといいな」＝「小学校の時のように仲良しでいようね」
ご参考まで！
カナダ 
