Recorded acoustic guitar and mic sounds too low in volume

There are ways of increasing the volume level of the track in GB after you've recorded it, but if the signal you've recorded is too low to begin with - what you're describing - then you'll also be increasing the noise as well as the signal. Better to record at a hotter signal to begin with.

This really happens outside of GB... you'll need to crank the juice before the signal enters the computer. Make sure that the mic is plugged into a mic input (rather than a line input), so your interface knows to run the signal through its mic preamp. I'm not familiar with your interface, but assuming you've got your mic plugged into the right input, you'll need to increase its level. As you increase its level, you should see the meter lights on the record-enabled track light up more and more. If they're barely lighting up, you know that your signal is weak.

Mic placement may also be an issue. Is your mic close enough to your guitar? Mic placement is an art and changing its position will change its sound. However, if you aren't getting a hot enough signal, you may need to physically move the mic closer to the guitar.

Also, since I believe that mic is a side address mic, make sure the "live" side of the mic is facing the guitar!

Good luck!