For a first time, great start! A couple of things if you don't mind. Bring the camera up to her level. Looks like you're shooting up. Crop above her chest. Have her wear a top with sleeves. Shoulders back. Ever since I read Benji's tutorial about no bare arms for portraits, it's the first thing I notice.
For the first time congrats. It's a little flat and your gf looks a bit tense. It's your job to make them look natural so try playing around with positions a bit but keep it clean or the shoot might turn into something else.
remember the closer the softbox the softer (bigger) the light. also you can manually set the cam for the correct WB value when using strobes, but at least adjust it in post if you leave the cam on auto