You aren’t handling the unsynchonized functions well. Also you’re using the deprecated upload button API.
It should be something like:
function saveProperties(){
//..your code code...
let toInsert = {
//the properties as you wrote
};
$w("#uploadButton13").uploadFiles()
.then(uploadedFiles => {
toInsert.url = uploadedFiles[0].fileUrl;
return wixData.insert("Properties", toInsert);
})
.then(results => {
//code code...
})
}