Hey Adam!

With the Playlist open (hit F5), hover your mouse in the grid area.

• Horizontal Zooming – CTRL + Scroll Wheel Up/Down
• Vertical Zooming – ALT + Scroll Wheel Up/Down

You can also zoom into the playlist without keyboard shortcuts..

Horizontal – Just grab the horizontal scroll bar at the very end, and you’ll see you can resize it!

Vertical – There’s a little square box in the top right of the FL Studio Playlist, right under the X (close), you can click + hold, then drag up and down to zoom in vertically.

You may also like this tutorial:  How to Navigate FL Studio Playlist EASY!

P.S. – The new revamp is launching today.. be on the lookout!