The South Americans will head into the last 16 on the back of three wins having overcome Nigeria 3-2 in their final Group F clash at Estadio Beira-Rio on Wednesday.
While a haul of nine points looks impressive, Argentina have yet to consistently find their best form and have, at times, looked vulnerable at the back.
Sabella concurs, although he felt that their showing against Nigeria was an improvement on 2-1 and 1-0 wins over Bosnia-Herzegovina and Iran respectively.
He said: "The team improved, had many chances to score, and could cause problems to the opponent.
"I am satisfied by the nine points we got but we still need to improve. I want to be champion of the world because it is a personal and longing of all Argentines."
While Lionel Messi's double, which moved him alongside Neymar at the top of the tournament scoring charts with four goals, will have delighted Sabella, he has worries over Sergio Aguero's fitness.
The Manchester City striker was withdrawn in the first half and it is unclear whether he will be fit for the next phase.
"Aguero has a muscle problem and will be assessed tomorrow (Thursday)," he added.
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