Can i just take propanolol before stressful situations and anxious situations ?

Short answer, Yes: Propranolol can be used for performance anxiety. Professional athletes, surgeons, & musicians have been known to use propranolol before performances. It is a blood pressure & pulse lowering med. So watch for low BP or a low pulse. Don't try to get your pulse to a target level on this med. It can provoke asthma or fatigue, and hide low blood sugar symptoms. Also good for migraine prevention.

Probably, but ask: Actually, this is a very common way to use it - but definitely tell your doctor that this is what you'd like to do. If there's agreement, fine. If not, you can press for reasons that may convince you. If they don't - consider looking for a new doctor but don't self-medicate. Also, consider CBT therapy to learn how to face stressful things. At your age, benefits of learning life skills can be huge!