Does the cup really not stretch you out at all?

I've been lurking here for a while now, and I'm pretty interested in cups - all the information and discussions here have been really useful. I'm a teenage virgin and slightly concerned about stretching. I know this has been asked before but I'm kind of making a point as well (ish).

Firstly, I think I would have issues with persuading my mum to let me use a cup. She won't let me even try a tampon because she swears that they stretch you out inside. She'll probably have even bigger problems with letting me use a cup.

And me? I'm not particularly worried about using tampons (heck, I've even tried two because we got some free samples from school...and they worked perfectly. But shhh my mum doesn't know about that.) Anyways, in terms of hygiene, cups sound way better. But with cups, I am slightly concerned about stretching.

I know everybody says that cups don't stretch you out and the vagina can go back to its original shape, but there are many stories about how people have had to stretch their vagina out to fit a cup in or that their cup has been easier to insert after a few months because they've got looser. Surely this means that they've been stretched out as a result of the cup and so the cup does stretch you inside? What do you think?

PS. I don't really know where to tag this except family & friends...