You're totally right. Here's how I've learned to navigate these situations. [EDIT] I started to write out specific advice, but as I was writing i realized there are more elements of nuisance to it than I could list in a short amount of time. So here's my top points:

• You can add qualifier words like "I believe X" rather than double checking.

• Act falsely confident in an amount scaled to how important the topic is. If someone making small talk asks what i had for breakfast yesterday, it's ok for me to confidently say "cereal" even if I'm a bit unsure, because it's not an important topic. But if someone asks me how much gas they need in their car to drive to the next town then I'll be very clear and tell them my level of uncertainty, like "I think it'll take around 5 gallons, but I'm not sure about that."

You can be confident that the right course of action is to seek further information. Double checking is a lack of confidence because you are not trusting your first check. If you seek other people's opinions, it's important that those people have experience and knowledge in the thing you are asking or it may seem like you will listen to anyone's opinion but your own.

If double checking your beliefs will mean you are then confident in them, do that double check before you speak. Make it part of coming to your conclusion in the first place, and then trust yourself enough to stick to that. That's true confidence. Worrying and asking for more opinions, or double checking after you have your conclusion just telegraphs uncertainty.