I was going to vs I was about to.

Question

10________ avisarte de que la fiesta se ha cancelado. I was about to warn you that the party is cancelled.Iba aEstuve aFuiEstaba yendo a Tuve que

I was completely thrown by the inclusion of the words "About to".

Iba a avisarte would just mean "I was going to warn you"

I was about to warn you should surely be: "Estaba a punto de advertirte" Not given as an option

Best

Ian

Answer

Hope someone picks up on this comment.

Answer

Hola Ian
"Estar a punto de hacer algo" means "to be about to do something" as you said, but in our lesson on
 Verb ir in El Pretérito Imperfecto + a + infinitive
we explain that this structure can be used to express 3  ideas:

actions that were going to happen
actions that were about to happen
planned actions or events

Depending on the context it means one thing or another. We give different examples in the lesson to show these different nuances.
The question you are pointing out has this specific meaning of "being about to do something", although it could also simply mean "was going to". 
For example, in this other sentence:

Menos mal que has llegado. Estaba preocupada. Iba a llamar a la policía.
(Thank God you arrived. I was worried. I was about to/was going to call the police.)

So there is an extra nuance here of being about to.
You could of course say:
...Estaba a punto de llamar a la policía.
That would also be correct.
Saludos 
Inma

Answer

Further explloration of the specific meaning of "I was about to do something" leads me to believe that "Iba a hacer algo, doesn't really translate into "I was about to do someting"  , more "I was going to do something, but not right now"Copy from similar query onnline below:Estar a punto de ...... is the 
construction you want to use. When something is very close to the point 
of happening, when something was very close to the point of happening.

Estaba a punto de ducharme ....

A native is not going to say iba a ducharme for I was just about, it just doesn't mean the same thing.

Answer

Further explloration of the specific meaning of "I was about to do something" leads me to believe that "Iba a hacer algo, doesn't really translate into "I was about to do someting"  , more "I was going to do something, but not right now"Copy from similar query onnline below:Estar a punto de ...... is the 
construction you want to use. When something is very close to the point 
of happening, when something was very close to the point of happening.

Estaba a punto de ducharme ....

A native is not going to say iba a ducharme for I was just about, it just doesn't mean the same thing.