1. Going To vs. Supposed To

2. Was going to
We use a past form of be + going to when we talk about a plan we had that may have changed.
A:You’re not staying out in this rain, are you?
B:Well I am going to, yes.
B definitely intends to stay out in the rain.
B:Well I was going to, yes.
B intended to stay out but may have changed his mind.

3. Was supposed to
To be supposed to is a common phrase that functions the same way a modal verb does. Modal verbs, also called auxiliary or helping verbs, add meaning to the main verb in a sentence by expressing possibility, ability, permission, or obligation.