This can be tricky if the tip has been pushed out the wrong way. Look at the edges, you go by the direction of the curl on the rim. If it's been pushed the wrong way, push it out the other way.
If you've placed in on wrong side out, you won't be able to roll it down. It will uncurl nicely, wrong way and it will be almost impossible to do - curling it out from the inside is pretty tricky, and you will know soon enough. And if you have started to unroll it that way, you're suppose to throw it out and get a new one because turning it the other way puts your pre-*** on HER side.