Hi Keith,
As John says check the fitting , this is particularly important by doors, fire places etc where it may not be too good.
If it is well fitted you would need to get it very wet to shrink it.
It's worth remembering it is the backing which shrinks so if you do not get the backing wet it will not shrink, so a good pre spray, agitate bad areas and extract, this should give you good results.
Cheers
doug