I keep getting g playful picnics - I have four that I have already accepted set is there a way to gift..

No, there is no capability to exchange or gift decoration at this time. You can sell or store (after storage ship is available in chapter 6) or keep. Many people will stop opening pink star boxes after they have enough of the Marvelous prizes that come from them. They save them for the next collection set, where any Marvelous cards received will have the prize from the new collection set.