I don't know...400-500 calories seems like a lot for only ~35min. of actual work. And if your not "bringing it", then 400-500 cal is definitely not
going to happen.
I like to think I have adequate knowledge with most things fitness and I have found that it is much more likely that the average person only burns 200 cal or so for every 30min of continuous
moderate excertion and that's being generous. To lose weight you need to sweat, sweat, sweat. Sweating is great indication of how hard your body is working and if you want results you have to work!! This is cliche' but totally true to any gym rat: NO PAIN, NO GAIN!!!
Frankly, if you really want to lose weight, in addition to your aikido class- run and run far. Start jump training/plyometrics and start pumping weight (make sure you push it during those last three reps). Do weights first then cardio. After 6 weeks switch to cardio then weights. The key to perfection of the body is keep it guessing!!
Good Luck and see ya at the gym!!!