It is far better to leave the audience with the last few bars of an exciting finale in their mind. There is no solo encore you could play that will not seem either lame, or pointless, or possibly even both.The audience will let you know if they want to hear more. They will either: keep on clapping and recalling you to the platform; or they will vocally demand more.The usual encore to play under these circumstances is a few minutes of the concerto finale. You would need to agree a starting point with the conductor beforehand.Good luck with the performance. I hope you enjoy yourself.Steve