it's ok for the either way, you can say 'I am supposed to..' or 'I was supposed to' .
It only depends the context you are uisng.
When you really want to meet a person and finlly made it, you can say, I just want to meet you so badly, otherwise I was supposed to stay at home for 'sex and city' this moment. .
本来打算 if my chinese interpretation is correct,it means he/she was trying to do something he/she had the intention to do but eventually he/she changed their mind doing something other than what they had intended to do earlier on...so by using the present tense i am supposed means changing of mind has not happened yet..the poster may still 打算 to do what he/she is supposed to do..
I suppose to go back China two weeks later.
I was supposed to go back China. (the idea was others', not yours)
I previously planed to go back China. (it's your idea)
I suppose to go back China two weeks later.
I was supposed to go back China. (the idea was others', not yours)
I previously planed to go back China. (it's your idea)""
i was supposed to go back doesn't necessary mean it's someone else's idea.it simply means that person was expected(either by him/herself or others) to take a certain action.the best way to put it is to say "i was supposed or intended to go back BUT....."
i previously planned .....would sound very unnatural if not weird in that context...just say i planned to go home BUT....(something cropped up and there was a changed of heart..)
as for i suppose to go back..well that's neither english nor chinese..
I suppose to go back China two weeks later.
I was supposed to go back China. (the idea was others', not yours)
I previously planed to go back China. (it's your idea)""
i was supposed to go back ...
You're right.
I suppose i should go back China.
I was supposed to do something, can be the person's expectation as well.
I planned to do something but... simple