Did I screw up? Rashquard sizing question.

I ordered a rash quard, im new to surfing.
It said to use my shirt size, which is Mens-Medium.
I am 5 5, 125 pounds.
Is a Mens-Medium too big?
Should I have settled for a small??
If i did this wrong then i basically lost $40, shirt + shipping.
, help please 
It said to use my shirt size, which is Mens-Medium.
I am 5 5, 125 pounds.
Is a Mens-Medium too big?
Should I have settled for a small??
If i did this wrong then i basically lost $40, shirt + shipping.

