how to correctly translate 我想你
In this case, miss equals to 想(念)，思念 while think of equals to 想到，想起. So 'I miss you' is the right choice. 'I think of you' means '我想起了你'. But sometimes 'I am thinking of you' is translated into ‘我想着你’.

When one say '我想你(+Adverbial)' or ‘我在想你(+Adverbial)’ as a sentence alone, it means that I miss you or I'm missing you. And when one say '我想你+...', it generally means 'I think you +...'. For example, 我想你很适合这项工作 means I think that you are fit to this work. Another example, 我想你在这个夜里 means I miss you in this night.