Jenny sent me a formal letter and a formal text :D
It was a formal occasion, so she wore a modest dress.
i wore my formal inside the house
Yes, your language appears formal and mature. Your sentence structure and word choice indicate a level of professionalism and sophistication typically associated with formal communication.
Tommy's lack of formal education turned out to be a great liability in his search for employment.
I am so sorry
That's a very beautifully written formal invitation.
Smallish is not a formal word to use, but you can phrase it this way "the baby hamster was a bit smallish compared to the little toy pet i have."
"Gigantic" is not technically a 'proper' word. It could be used in a sentence like "The apple was gigantic", but that is not a formal sentence and could not be used in an essay for example.
Several marine institutes bankrolled his search for the sunken ship.(formal writing should use the synonym financed)
The officials of the city sent out an edict on their formal stationary that no city employees were to take unallowed breaks on the job.
Can you use the word concluding in a sentence? Done.
You can use the word Truss in a sentence like this.