The help file includes the example below.According to it, your implementation looks correct.
Rem
IncBin embeds an external data file in a BlitzMax program that can
then be read using the "incbin::" device name.
End Rem
' code snippet from demos/firepaint/firepaint.bmx
Incbin "stars.png"
Local stars=LoadImage( "incbin::stars.png" )
Rem
IncBin embeds an external data file in a BlitzMax program that can
then be read using the "incbin::" device name.
End Rem
' code snippet from demos/firepaint/firepaint.bmx
Incbin "stars.png"
Local stars=LoadImage( "incbin::stars.png" )