It sounds to me like you're doing great, especially for a beginner! 30 mins in the morning plus some afternoon stuff is really good. (Is that another 30 mins in the afternoon?) I don't know how Curves works, but eventually I think you'd want to work up to 45 mins of cardio and then maybe even 60 mins of cardio, plus strength training, but 30 mins is a great start.
It's also important to remember that 'enough' is really as much as you can possibly do and STICK with. You could work out 8 hours a day like the Biggest Losers, but you'd burn out in no time and you just wouldn't be able to sustain it. Give yourself credit where credit is due and set yourself reasonable but ambitious goals