When you create new partitions you need to split one of the existing to two, as usually all the space on your mmcblk0 is allocated already. Normally on a Harmattan device (N9/N950) you'd use your first partition which is your MyDocs, and split that. If you have just very little installed on that partition it is probably safe to do just like that, otherwice I suggest you backup it first and then repartition, and finally restore the backup.