Learn English – Sins are made/done

While I agree with J.R.'s comment that your sentences are basically fine, I think at least two could be better.

"I'm concerned about what my mother eats."

is not a problem at all.

"I'm concerned about others a lot."

is less than optimal for two reasons. First, my preference is to use very concerned about others rather than concerned about others a lot, which sounds awkward to me. Second, if you mean what you say ("I tend to think that they are doing all right or everything is all right with them all the time"), then your sentence is actually contradictory, and you don't mean what you say. If you were concerned, you'd be worried that they weren't okay, but you're not worried.

"I'm concerned about my test for tomorrow."

I think it'd be more natural to say "I'm worried about tomorrow's test. I'm usually concerned about others' problems but I worry about myself and my problems.

Either of these might work:

• The third letter is sideways.
• The third letter is rotated 90 degrees.

I suppose you could also say:

• The third letter is tilted at a right angle.

but I don’t think you’ll have as much luck with that one on Google.