Hello Red Dog,
Sounds like you are trying to print cut lines that have not been given any "weight". Those red lines are for the cutter to follow, but if you want to print them, first select all the lines, then use the LINE STYLE (fifth icon down on the right hand side - looks like three parallel horizontal lines - top one is dashed, middle is a thin line, and the bottom is a bottom is a fat line). You can also, while you are there in Line Style, assign different colors to lines/objects that you individually select, and then you are able to selectively send those colores lines to be cut (or sketched, etc) using the Send/Lines tab. In this case, if you'd like to print the design, your Print Preview will show all the colors, as will your print.
Suggest you become familiar with the Line Style as well as the Fill tool just above the Line Style icon - you'll be using them frequently as you grow with Studio.
Gene K
EDIT: The weight (thickness) you give to a line has no bearing on the cut line - that's still present. The line you made is for your visual benefit.