I would say that technically it's right, but it's not common used in this way. By the way, depending on the context, 都 means "All the time" or "All/Everything". In your sentence it means all the time.

“在”“很”不一起用，在is "-ing"，means now, in a short time；“很想念”is a contion(situation)last for a long time，所以是矛盾的。so“我在很想念你”is incorrect,you can say"我在想念你"“我很想念你”。 I hope it make sense. And also,I think when you say "我在很想念你"，every Chinese knows what you want to express, just remember the correct expressions, learn as more expression as you can. Grammar is difficult,especaially Chinese grammer.

hello,Elizabeth the chinese language is extreamly rich.there are many meanings about 都。it means all or all the time,perhaps it has any other meanings,and i am not clear about it.if you want to know the fully meaning,you can look it up in achinese dictionary.都is not commonly used in our daily life。we always use 一直or 一直都instead of 都 you can say that:我在想你。我很想你。念is not always used here.do you understand it?sometimes the language has fix structure and uses.perhaps something there is no why in it.if you learn more,you will know.

我想念你。 我很想念你。 我在想念你。 我時時刻刻在想念你。 我時時刻刻 "都" 在想念你。 (時時刻刻＋肯定語) 在此 "都"表強調語氣, 指全部時刻 即 "all the time" 之意 我無時無刻不想念你。 (無時無刻＋否定語） 我們在想念你。 我們 "都" 在想念你。 在此 "都" 表強調語氣, 指第一人稱複數全部 即 "all/everything" 之意 "都" 在當副詞 指數量多少的意思時 為"概括全部" 的意思 指前一詞的全部

Yeah I'm afraid so it's not very correct. 我 们 都在想你 >>> WE all miss you. 我 一直 都在想你 >>> I've been missing you all along, all the time. So see, that's the 'all'. 一直 means always.