我们明天下班以后一起看电影吧 should be correct too. I'm a native speaker and couldn't figure out why I was wrong haha.
I mean, "電影吧" was listed as one word instead of two in this problem. I guess we're supposed to go to the "movie bar," 哈哈哈哈哈！
Also a native speaker here, I got this question twice and agreed with you both times.
It is accepted now, thanks for all the reporting.
我们 and 明天 should be swappable in first and second place at the beginning of a sentence.
Yes, it is accepted now.
Translating from English, not sure how I'm supposed to deduce that “let's go" doesn't translate into something with 去 and apparently turns into 一起.
The "let's go" is actually indicated by the "吧" at the end. "一起" just means together. I think that it's also acceptable to use "去看电影吧"。
Why do you need 一起. Would it be acceptable to leave it out?