So, um, you might not like my answer.
Personally, I've seen the best progress in myself when I don't do 'cardio' at all (assuming you're talking about elliptical/treadmill or similar).
Instead, I enjoy a combination of resistance training and intervals/sprints. If I were you, I'd trade out 3x45min of cardio a week for 3x30min weights + 15min intervals. If you're most comfortable with the machines then start there - using machines is WAAAAAY better than never lifting because you avoid free weights like the plague.
In terms of anabolic stimulation (activity that helps you keep/build muscle while losing fat) and EPOC (Excess Post-Exercise Oxygen Consumption, ie. 'speeding up' your metabolism for up to 24-48hrs after working out), the literature I've read suggests that resistance training and intervals have a better bang-for-the-buck than traditional 'cardio' when trying to lose fat.
Even if you were to trade out ONE of your workouts a week for lifting instead of cardio, I think you would see good results over time. Building strength helps prevent muscle while losing fat, adds shape to your body, and generally increases your capability during physical activity.
Here are a few posts where I've touched on lifting exercises to start with (plus extra information from other members, which is also great!):
Looking for exercise advice
3 day/week Lifting Routine suggestions
'Hope that helps! I'd love to hear what you decide to do, and how it's working out for you after a few weeks.
But most importantly, have fun.