Translation:I am going to learn English.
It's not exactly like that. [Am + verb+ing] is usually expressed with the -ています form (which hasn't appeared at these heights of the course).
Though that, every language has different sentences where present or gerund are used in an idiomatic way, so it's normal that some sentences that in English are expressed through a gerund in Japanese are expressed through a present tense, and vice-versa.
It doesn't matter that en:"I am verbing." translates to jp:"verbています" though. If we're translating a given phrase in the direction Japanese->English, then we should accept that it is more natural to say in English, "I am verbing." And in fact, several other Japanese->English translations -do- accept "I am verbing" as an answer.
The strict distinction should only be required when translating English to Japanese, because Japanese is the language where the distinction matters.
Direction of translation is an important context that this course all too often fails to consider.
This comes back to how Japanese basically has a future tense and a "non-past" tense. "Naratteimasu" would imply you are currently in the state of learning in that moment. "Naraimasu" is exactly what I described as just non-past. In terms of English it would translate as "I learn/am learning" depending on context.
In short, try not to think so literally when up against gray areas like this. Go with what's implied rather than what's literally a word-for-word comparison.
Basically the difference is that ならう means learn and べんきょうする means study, and yes, the latter does generally imply more explicit effort, not only in terms of the etymology of the characters used to write the term, but also as a general educational concept. A native speaker might be said to have learned his/her native language during the first years of life without any explicit study. 言語習得 (げんご しゅうとく) is one of the terms used for language acquisition (whether native or other) where げんご means language and the first character of the word for acquisition しゅうとく (literally gained / acquired through learning) is the character for ならう, but pronounced here in its Sino-Japanese reading (おんよみ ) of しゅう.