Going to isn't always gonna

Going to can not always become gonna .

Going to + V: I'm gonna leaveWhen going to refers to the future, in spoken English it turns into / gənə /, transcribed very informally as "gonna". Gonna is not used in written English.  It is nothing more than a rough approximation of the pronunciation. The two vowels / ə / in gonna, which are spoken very quickly, are the same sound you hear in, love, the indefinite article a and but. The "t" that was in the original going to simply disappears.  I'm going to eat turns into I'm gonna eat; They are going to sleep becomes They're gonna sleep. What are you going to do? = What are you gonna do? or very informally, Whatcha gonna do? Is he going to fly to Seattle? = Is he gonna fly to Seattle? Gonna, however, is not mandatory. You can continue saying going to before an infinitive and nobody will mind or even find it unusual.

Going to  + a destination. He's going to Rome (gonna is not used here)

But going to is not always followed by a verb.  It can also be followed by a destination. I'm going to Natal next week. They're going to the theater. In these cases, the pronunciation doesn't change. *He's not gonna school tomorrow won't cut it, I'm afraid. We need to say He's not going to go to school tomorrow.  When going to is followed by a destination, we may be talking about a future action, but it is also possible that the action is happening right now and we are using present continuous, as in  He's going to the bakery right now.If you want to use gonna with a destination, the solution is simple: use going to go to + where you are going. For example, I'm going to go to the beach = I'm gonna go (go is an infinitive) to the beach. In short, you can choose betweenI'm going to the beach (not gonna)I'm going to go to the beach (with gonna.)

Going + Verb + ing. He's going skiing. (Not gonna)
Another situation where you can not use gonna be before verb + ing. Many recreational activities in English take the form go + verb + ing: go shopping, go hunting, go running, go camping, go skiing, go skating, and so on. . In the sentence "I'm going skiing tomorrow", going retains its original value; we can't use gonna. But of course, you can use going to + go + verb + ing with gonna. I'm going to go skiing on Friday can turn into I'm gonna go skiing on Friday. The use of going to go, that is, two forms of go one right after the other, is totally normal in English, so don't be shy: go ahead and do it!