Translation:I think your shirt is too small.
I wonder when this course will ever have some changes in the program added to correct and accept typos. I'm doing the French course too, and it is so much more advanced. If you miss a letter due to typing it still gives you full marks and points out the typo you made. But not this course. They seem bent on teaching us English here more often than Chinese.
An amusing thought, but no, I think it just emphasizes that it is too small, not just very small.
[Edit: TY Looli23 - we are all learners here :)]
了 gets used in a number of different ways, and I think this particular exercise is about one of them where it is used in a pattern of 太[adjective]了. This changes the meaning of 太 from 'very/extremely' to 'too/excessively'.