We use Present Continuous (am / is / are + verb-ing) to talk about fixed future plans.
It is already arranged (meeting, ticket, agreement).
Usually has a time expression (tonight, next week, this weekend).
Forms
Affirmative:
Subject + am/is/are + verb-ing
Negative:
Subject + am/is/are + not + verb-ing
Question:
Am/Is/Are + subject + verb-ing?
Important Difference
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Going to → intention (just a plan in your mind).
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Present Continuous → arranged plan (fixed and organized).
Easy Rule:
Fixed plan + time = Present Continuous.