I don't think that's too much, but it also depends on your restrictions. You should really make a plan and stick to it. If you're really that worried about it, go do 4 sets of this: Jump up and down (like jumproping) for 1 minute, rest 1 minute, jump up and down 1 minute, rest 30 seconds, jump 1 minute, rest 30 seconds, jump 2 minutes, rest 1 minute. That should burn around 200 calories, or about half your lunch.