if a person has URI and plays the high notes with french horn will something bad happen

If by URI, you mean Upper Respiratory Infection, the answer is no.

are you sure because im in band and I cant risk my throut

I'm pretty sure, but I'm not a doctor. If you're concerned, please call your doctor's office tomorrow.

If a person has a upper respiratory infection (URI) and plays high notes on a French horn, it may not directly cause anything bad to happen. However, there are a few factors to consider:

1. Discomfort: Playing high notes on any brass instrument requires a significant amount of air pressure and control. If you have a URI, you may experience discomfort or difficulty in producing the necessary air support, making it challenging to play.

2. Exacerbating the condition: Engaging in physical activity, such as playing an instrument, while having a URI can potentially worsen your symptoms or prolong your recovery time. It is generally recommended to rest and avoid strenuous activities when you are ill.

3. The spread of infection: If you are experiencing a contagious URI, playing an instrument, especially one that involves blowing air, might increase the chances of spreading the infection to others.

To determine the severity of your URI and its impact on playing the French horn, it is best to consult with a medical professional, such as a doctor or nurse. They can provide you with more specific guidance based on your personal health condition.