What happened to your other 7 pins? You have 20 IO, D0 -D19 (A0-A5 are D14-D19).
Use a MAX7219, wire your LEDs up as if connected in a matrix, but arranged physically in a strip, then send simple SPI commands to the MAX7219 to light them up in order.
$1.25 at taydaelectronics.com.
The digits in this unit are driven by a MAX7219, along with pairs of LEDs on the outer bottom boards.
The empty looking sockets at the top middle are actually the breakout from the MAX7219 to the digits.
Use a daisy chain of shift registers to control 1 LED on each output.
This board holds up to 12 shift registers to control 96 LEDS.