When I was watching the film, I felt like I was on an adventure with the main character.
映画を観て主人公と一緒に冒険している気持ちになりました - When I was watching the film, I felt like I was on an adventure with the main character. (I was just so excited / I felt like I was a part of the film / It was so believable)になると思います。
映画を観る - watch a film / watch a movie
主人公 - main character / protagonist / the star
と一緒に - together
冒険 - adventure
気持ち - feeling
口頭で言うなら - When I was watching the film, I felt like me and the star/main character were on the same adventure together. も大丈夫だと思います。
While watching the movie, I felt as if I was on an adventure with the main character.
おっしゃられている内容は、以下のようにも表現できると思いました(*^_^*)
While watching the movie, I felt as if I was on an adventure with the main character.
「映画を見ている間、まるで主人公と冒険しているように感じた」
feel as if 「まるで～のように感じる」
以上です。
少しでも参考になれば幸いです(*^_^*)
イギリス 
日本 
