That should work better.
I've generally found that it's better to err on the light side with batteries. A plane that size probably won't need more than an 800mah and may fly better with something smaller. The good news is that those batteries are cheap, so buy a couple. Again, recommendations from people who have built this plane can be very helpful.
On the topic of battery size- more capacity doesn't always equal more flight time. With more weight, you'll need more power to stay flying, which uses up your capacity faster. There is a happy place where that balances out, but IMO it shouldn't be your biggest concern. Build the best flying plane possible and enjoy it. If you only get 5 minutes of flying per charge, that's ok. Buy multiple batteries and a good charger.