Should be 一人だけがいられる just to be grammatically correct (because it's a person, not an object). Still, that's only if you feel the need to go the super-literal route. I personally don't think it's hitting the mark at all like it seems you want it to. I'd also bet money that the line they used in the Japanese movie is quite different, because 一人だけがいられる sounds like the number of people allowed to use the break room or something equally mundane.
I don't mean to sound like a snob, but one thing I see a lot of is signatures and profile-text in forums where the member obviously went to a place full of Japanese-language students and asked how to say something, and they gave him a half-baked literal translation that he then used and it's just weird. We've all seen Engrish before, right? Honestly, it goes both ways.
If you're really serious, either get the exact movie line or check with a native speaker. Trust me, I've done both English and Japanese subtitles working side-by-side with Japanese people, albeit on an amateur basis, and you'd be surprised how much some things have to change to work much at all. Also, I teach a lot of private one-on-one lessons with Japanese people, and they ask me "how do you say x in English?" all the damn time. My answer about 50% of the time is "you don't". What I mean is, you shouldn't focus on recreating a Japanese expression in English, but rather on what English-speaking people say at times when they are in the same kind of situation and/or feel the same kind of emotion. This, too, goes both ways.
The only reason to go literal is if you're making this for native English speakers who know a little Japanese. I see shitty English in advertisements all around me day in, day out, and it used to drive me nuts. However, I've come to terms with it on the basis of accepting that it's not written for me in the first place, but rather for Japanese people who know a little English. In other words, it functions like it's supposed to for whom it is supposed to.