It's not very stretchy/elastic, a little crumbly, is there any way to salvage it??

I've made it many times without fail and this is the first time it hasn't been right

Try kneading in a little bit of shortening or some glycerin. I've had it come out like that a couple of times, without being able to figure out why.

I've added more melted marshmallows when it's too dry (and shortening or water don't help).

Thanks for the tips, I've added some shortening and it's not as crumbly and more smooth...just worried about when I roll it out and put on the cake, will it tear if it's not that stretchy?

I swear I did everything the same, don't know what happened

Try rolling it out and placing it over a box edge or your finger tips. If it cracks there, you might want to loosen it up more.

The only time I had MMF do this was when I used miniature marshmallows instead of the regular marshmallows. I don't know what the difference was, but that was the only thing I did different. I know some recipes call for the miniature marshmallows, but I have always used the regular.

*editted to add- I fixed the problem by adding more marshmallow and it came out fine.