I've attached the part and drawing, I want the piece to have an arc length of 37-1/2" which when the piece is rolled that what the outside length is, which is correct. However when I use the flat pattern in the drawing it says the length of material is 37-5/16" doesn't make sense to me. Maybe it's correct I'm not sure.

I've also changed so I dimension the inside arc with the arc length and flip the way the sheet metal extrudes and it changes the arc length to 37-15/16" when rolled and 3-11/16" when flat. 

Does this seem correct?

Thanks.