Tampons don't contain asbestos or anything else harmful

How does it fit inside you? Um, your vagina is a lot bigger than a tampon. Remember that a penis can fit inside and also a baby can come out! Look at a newborn's head and you'll see why a tampon fits LOL
Why not try inserting a finger into your vagina first, just so you can reassure yourself that a tampon will fit? As for losing the string, well, you can't. It hangs outside of you. If for some reason it gets pushed up into your vagina (this has never happened to me), just stick your fingers in and fish it out. The tampon can't get "lost" anywhere. Your vagina is basically a closed tube up on top. The cervix protrudes into it, but no way can a tampon migrate through your cervix.
The tampon also doesn't get "stuck." Just pull on the string and it comes out.
There's really nothing to be afraid of. Try using one. Remember, you're in control, so you can't hurt yourself. Stop if it feels uncomfortable. I had a little trouble inserting one the first time. I was aiming it straight up, instead of at an angle towards the small of my back.
Good luck!