Yes, it’s perfectly acceptable. “Learnings” is simply the plural form of the noun “learning,” which means “the act or experience of one that learns,” “knowledge or skill acquired by instruction or study,” or “modification of a behavioral tendency by experience.” This plural form of “learning” is different and shouldn’t be construed as the grammatically wrong plural of the gerund “learning” (a gerund has no plural form) or the grammatically wrong plural of the progressive-tense “learning” (this form likewise has no plural form).
As to the usage of the idioms “on my mind” and “in my mind”:
“On my mind” (using the preposition “on”) is used to indicate that one is thinking about something or that one’s thoughts are occupied in some way, as in “On my mind during our meeting was the possibility of appointing you ambassador to Surinam” and "It was on my mind to end the discussion outright."
In contrast, “in my mind” (using the preposition “in”) is a discourse marker to indicate that what’s being said is one’s opinion or presumption, as in “In my mind, considering that her IQ is just above average, her rabid supporters should stop foisting her participation in that highly demanding talent contest” and “In my mind, the best choice is the fifth applicant.”
