Here are some tips that will help you reach your goal:

First, make sure you're consistent with your studies. Set aside a specific time each day for studying and stick to this schedule as much as possible - it's the only way you'll be able to make real progress within such a short timeframe. Additionally, don't rely on just one resource when learning BSL; use textbooks, online resources, YouTube videos and more for maximum learning potential!

Second, practice speaking with native signers whenever possible. This will help improve both your fluency and pronunciation skills faster than if you were practicing alone. You can even find virtual language exchanges or join local signing groups where you can connect with others who are also trying to master the language.

Finally, remember not to be afraid of making mistakes - everyone does at first! Making mistakes is part of the learning process; embrace them as an opportunity for improvement instead of letting them discourage or frustrate you. With these tips in mind and plenty of hard work, achieving mastery over BSL in 12 weeks doesn't seem so daunting after all!