You don't sound stupid at all. I think, if anything, you lack self-confidence and everytime a coworker calls you out on an error it cause you to constantly second guess yourself. I do the same thing all the time. We are our own worst critics.

You have to jump in and ask the questions. Use, "I know you're busy, but please show me this..." or "As soon as you get a second, could you help me with this." You're all on the same team and are working towards the same goals. Coworkers are supposed to help their fellow coworkers and in time it is only to their benefit since you'll be able to share in the workload.

And try not to beat yourself up. Mistakes happen, we are only human after all. There is almost nothing that can't be fixed as long as you stay honest and upfront.