Make a model in blender, exported to STL, looks great, nothing prints!

I must be missing a step here (and pardon me but it's Day 1, so super-noob). I made a model of an arrow in Blender, exported it to STL. If I double-click it I get a nice preview of it, and it's about 50mm, the size I'd expect.

When I load it into BoXYZ, my printer's interface, I can then slice it, which works. But it winds up with no work to do - prints nothing. It says the object is manifold.

I'll attach my STL file, maybe someone can see something brutally obvious. Thanks in advance for any help!

Cheers,
Dave

Solved it! Turns out that the dimensions in Blender are ignored. I had set it to 1.0" and the default unit appears to be mm, so it came out as 1mm.

I changed that to 50 and now it's printing...