Hi Robin,
thanks for your question. As Derek Law points out, Survey123 is limited at the moment to capturing points, although adding support for lines and polygons is planned to be implemented in 2017. I would suggest you vote for Improvement idea for survey123: create lines and polygons
Also, in case you had problems trying to add your questions to the Survey123 for ArcGIS Group make sure you follow the Survey123 Group. The Survey123 Group is members-only, meaning that you have to join the group (follow it), if you want your questions to be shown in it. The screenshot below shows the button in the banner that will help you join the Survey123 Group.