Proper infill settings


Hello, I was trying to print a whistle the other day using Cura. The product description stated that the infill percentage didn’t really matter, but he printed with 100% infill. I didn’t want to use as much material so I set it to 80%. But when it started printing, my Anycubic i3 Mega printer started filling in the designed holes and extruded cuts of the model that are necessary in its sound functionality. I suspect it was an infill issue, but I’m not for sure. How do I fix this so that the holes are not filled in?

This is the model