The outline svg needs to be a single differential path (and is quite difficult to make successfully.) Search in the forum for “pcb slots” will turn up instructions such as this one
Alternately you could post your outline svg and one of us may be able to help some.
“Worst case scenario” which isn’t actually that bad depending on what you’re requirements are - is to just use the HOLE part in fritzing to put holes where you you need - eg mounting screws, or some other circular hole size required.