Only your supervisor can answer your question. What did he/she say when you asked? If you haven't asked, then you should schedule a meeting (perhaps after taking a few days to calm down a little and think things through) to discuss it.
Also ask for specific suggestions for improvement and leave the meeting with a plan for meeting specific goals along the way toward the improvements your boss is looking for. Be sure to find out how and when your performance will be re-evaluated. You may want to touch base on a regular basis with your manager or an educator or a mentor/preceptor person of some sort to give you some ongoing guidance and feedback.
The important things are:
1. to understand the nature of the problems that your supervising is talking about
2. to have a plan to address those problems
3. to get regular guidance and feedback regarding your performance in the future. Don't wait until your next yearly eval to address the issues.