Both cardio and weightlifting play vital roles in weight loss. Weightlifting helps as you mentioned, by building muscles which in turn burns more calories over the course of the day even when you are not in the gym. Cardio on the other-hand is a great way to burn calories in bundles in one workout. Your problem seems to be that you only have 3 days a week that you can get to the gym which doesn't allow to work cardio on the days that you are not lifting.
Because of the above I would really recommend doing HIIT type workouts. High intensity interval training allows you to burn a lot of calories while you workout and also build some muscle which will help you burn calories even when you are out of the gym. Now obviously this won't build as much muscle as as would a regular weightlifting session, but given the fact that you have a goal of losing FAT and not WEIGHT and only having 3 times a week to workout I think that this is your best bet.