brianduffy is it slightly out of tune or dropping out of tune a large amount?
I find my violin goes slightly out of tune daily I think that is due to humidity and how warm it is. IF it drops out of tune large amounts it due to the Pegs working their way out of holes. When you tune with the Pegs you need to Press inward as you turn.
Also IF the strings where not put on correctly it could contribute to it not Griping properly.