Nice friend of yours but sorry, it will not work. Previous versions of the watch which are 38mm only work with either those marked as 38 or bands made for the same size of 40. Same is true for the 42, they will work with the 44 and vice versa
To be clear, the attachment mechanism for the bands is universal between all Apple watches released thus far (and likely far into the future), so yes, it will fit - it will attach securely and connect and disconnect easily. But the watches and bands are available in two basic sizes, effectively (though not called) "small" (38 or 40mm), and "large" (42 or 44mm). Bands from either will fit the other, but will not look right. A "small" band in a "large" watch will look a little too narrow, while a "large" band in a "small" watch will overhang the sides and just look wrong. I'm sure there are people who do it, but I wouldn't recommend it.
The edges of the 42mm band will stick out slightly on a 38 and 40mm watch. I tried my 42/44mm sports band on my mom’s 40mm and the edges stuck out just a bit. However, the band does lock in place if you don’t mind the edges sticking out.