Is this the right usage?
For "fixing to (do something)", that depends.
If I am writing an academic paper or a business-related email, then no.
If I am in Boston, or Chicago, or San Francisco
and I don't want to sound out of place,
then no.
But if I am living in the South of the US and I am having casual conversation, then "fixing to" might often be just the right word to use.
"Fixing dinner" is much more prevalent than "fixing to (do something)".
I say this because I don't think it would feel out of place in any of the (northern and eastern US) places I have lived (though I would imagine it would get the heaviest use in the South).
Still, I probably wouldn't personally use that phrase in formal, written English.
english.stackexchange.com/users/449/Kosmonaut
"Fixing to ..." is common usage in the southern US, meaning "about to" or "preparing to" do something, but rarely if ever at the beginning of a sentence.
Perhaps in answer to a question: "Whatcha doin', Pa?
" "Fixin' to hunt me some possum."
english.stackexchange.com/users/67/moioci
Even though I can be offended by incorrect grammar to the point where it might be obnoxious at times, I still embrace local colloquialisms.
Having been born and bred in the Deep South (US), I use "fixing to" regularly.
Yes, it means "about to".
However, since we don't pronounce hard g's at the end of these expressions, it would be pronounced "fixin’ to".
english.stackexchange.com/users/48639/Mary
It's also appeared in song titles, most notably I-Feel-Like-I'm-Fixin'-To-Die I-Feel-Like-I'm-Fixin'-To-Die is the second album by the influential San Francisco psychedelic rock group Country Joe and the Fish, released in 1967.
The title track remains one of the most popular Vietnam protest songs from the 1960s and originally appeared in a 1965 7" EP titled Rag Baby: Songs of Opposition.
english.stackexchange.com/users/1146/Antony Quinn
If I'm fixing (or fixin') to do something, fixing is an adverb, answering the question of "when" you're going to start doing something.
I'm from the South (Savannah, Georgia) and this is common usage in those parts.
This "fixing" is completely different from the verb "fixing" in this sentence:
"I'm fixing the broken gate" -
How about this one?
"I'm fixing to start fixing the broken gate".
The first fixing is an adverb, the second one a verb.
Miriam Oglesbee Ellison
english.stackexchange.com/users/175397/Miriam Oglesbee Ellison
Um.... That's colloquialism.
Southern people say "fixin to" while African American people tend to change the expression to "fittin to.
" They mean the same thing.
It essentially means to prepare to do something.
"We were fittin to go to the park, when, suddenly the weather changed, as did our plans."
english.stackexchange.com/users/89502/Sarah s.
Use of  fixing to  at the beginning of a sentence is prevalent in the southern states of Amerca. Is this the right usage?  And is this only a southern US thing?  Examples:   Fixing to call her.  Fixing dinner.  Fixing to leave the house.
"Fixing to" at the beginning of a sentence
english.stackexchange.com
<dialects><slang><colloquialisms>
english.stackexchange.com/questions/3033
english.stackexchange.com/users/1158/GBackMania
Whether or not "fixing to" can be used correctly at the beinning of a sentence will depend on the context. It is generally agreed that in a formal document, this usage is not acceptable. However, in colloquial speech in the Southern US, this is very common and means "about to". This is a colloquial expression commonly used in the Deep South of the US, with many variants and examples in songs.
Whether or not "fixing to" can be used correctly at the beinning of a sentence will depend on the context. It is generally agreed that in a formal document, this usage is not acceptable. However, in colloquial speech in the Southern US, this is very common and means "about to". "Fixing to ..."  is  common usage in the southern US, meaning "about to" or "preparing to"  do something, but rarely if ever at the beginning of a sentence.  It essentially means to prepare to do something.    
"Fixing to ..."  is  common usage in the southern US, meaning "about to" or "preparing to"  do something, but this is rarely if ever used at the beginning of a sentence.   This usage of the word "fixing" is common in the Southern USA and means "getting ready" to do something.
This is a colloquial expression commonly used in the Deep South of the US, with many variants and examples in songs.
"Fixing to ..."  is  common usage in the southern US, meaning "about to" or "preparing to"  do something, but rarely if ever at the beginning of a sentence.   It essentially means to prepare to do something.    
This usage of the word "fixing" is common in the Southern USA and means "getting ready" to do something.