Regarding the Potentilla, there are 2 types - one is Potentilla fruticosa, which is a deciduous shrub, the other is P. nepalensis, of which you have a variety, and which is an herbaceous perennial.

thanks for your answer,i was going to get rid of it.but i think i will keep it after all.the mail order company that i got it from no longer sold it and could not give me any advice about

Best place to plant your Potentilla is somewhere sunny where it can sprawl its long flower stems without being a nuisance. I've got mine on the edge of paving. Cut back spent flower stems to keep it a bit tidier during the season.

I was told recently that not all the herbaceous potentillas are straggly Bamboo, and as I have the same problem I was hoping to find some that were upright - should I give up and grow cistus instead?

There are about 15 different types of Potentilla, Steragram - the ones you find easily for sale are Potentilla fruticosa varieties (the shrubby one) and P. nepalensis varieties such as 'Miss Willmott'. Of the other 13 types, there are some which have short flower stems. P. cuneata, for instance, has virtually stalkless flowers, and is good in a rock garden.
As you've mentioned Cistus, which are evergreen shrubs, usually making 3 to 4 feet in height, maybe you thought you'd bought the shrubby Potentilla? How tall do you want your plant to be?

Oh I didn't mean cistus then. I'm thinking of a low growing well behaved herbaceous plant with small grey leaves and yellow, pink red or white flowers. I had always called these rock roses but must have been mistaken. When I bought the potentilla I was thinking it wold be one of the short stemmed ones. Ignorance is a terrible thing!

You're thinking of potentilla fruticosa varieties then - such as P. 'Red Ace', P. 'Goldfinger', P. Elizabeth. They're shrubs, so won't be in the perennials section at the GC.