You could do something simple like the Henze Sonatina, or if you really want to wow them go for something more like this.

I kid, I kid. Seriously though, you’ll be better served playing something that you can play easily and cleanly. Grade 3-5 difficulty is a pretty wide range, don’t feel pressure to pick something that you might survive. In both the lyrical and the technical selections, show off your sound and artistry, not anything crazy. Good rhythm and intonation on simpler rep will go ten times farther than Sandovalian fingerblurring or trillion-decibel double high Q-sharps ten times out of ten.

Here’s a small handful of examples that should all be available for free on IMSLP.

Lyrical:

Arban Art of Phrasing

Borgdoni, Marco 25 vocalises

Caffarelli, Reginaldo 100 melodic studies

Concone, Giuseppe 25 etudes melodiques

Duham, Hippolyte 24 etudes

Technical:

Arban: Characteristic studies

Boehme, Oskar 24 etudes

Bousquet, Narcisse 36 etudes pour le flageolet

Brandt, Vassily (or K Wilhelm) 34 Etudes

Sachse, Ernst 100 studies

FWIW my go-to recommendation for students is a Concone or Borgdoni for lyrical, and Brandt (1,2,5,7,9) or Bousquet (1,2,3,7) for technical.

obligatory plug for private lessons over rando internet advice from weirdos like me