Assuming you mean shrubby potentilla, you can trim it now if you want, but you'll obviously be cuttng off the flowers.

It won't do it any harm if you don't mind losing those flowering branches

ok thank you its not very big at the moment but flowering lovely but it looks like it needs tidying up just a little at the sides

They are 'untidy' by nature. With a bit of judicious pruning they can be put into shape. But, I just let mine do what it wants.
If you plant something like a spreading Geranium (Anna Folkard comes to mind), it will help disguise the unruly behaviour.