Lots of people think very negatively about failure and mistakes. But a mistake is an opportunity to learn. Do not feel defeated about a goal you failed to reach, instead look back at what happened, look at where you struggled, where you succeeded. Every failure, every mistake is an opportunity to improve.
The only real failure is to give up. You're cementing your own defeat.
We're coming up on the big trial time: February and March. Most people give up and quit, and lock in the big failure. To succeed, just hold on. Just keep going. A black belt doesn't become a black belt by a single superhuman act. They do something entirely human every single day. The biggest deciding factor in a black belt is determination.
Karate is not made for people who are superbly athletic. It's not made for big men. They don't need to defend themselves. It's made for common people. Most black belts are not people with special coordination skills or exceptional physical skill. They are people who do not give up. More often than not, someone with 'talent' will give up when karate gets too difficult. Since they have natural talent they've never had to struggle. At the first sign of difficulty, they quit. Black belts persevere.
You can all be black belts. The goals you have set are are difficult, but they are not impossible. You can do it!