Although it should be accepted, a blouse is more specific and closer to un chemisier. un tee-shirt for a tee-shirt and un polo for a polo. Women, when they are not wearing dresses or tee-shirts, tend to wear blouses / button-downs / or dress shirts, but that is not always the case when describing just a shirt. You could describe it une chemise en cuir / de cotton / en soie / etc...
Updated to allow for an optional second article. Please keep in mind that while additional articles after the first one are optional in English, they are mandatory in French.
Please allow up to a week for the system to recognize and accept the changes made before reporting. If after a week it is still counting it as wrong, please report it and leave a message here. Thanks!
I think this is called a "schwa" in French,I've also wondered about the same and did some search. Please check the link for more info : https://frenchcrazy.com/2013/04/the-french-schwa.html/