If I remember correctly =記憶が正しければ
If I remember correctly, that's the first movie I saw in the theater =記憶が正しければそれは映画館で初めて観た映画だ
I'm pretty sure =結構自信がある
I could be wrong, but I'm pretty sure that that's the first film I've seen in the theater =間違ってるかもしれないけど、多分その映画は初めて映画館で観た映画だ