I think you have nerves, sort of like cold feet. Someone believed in you enough to offer you the job. Do it. The job itself is the best practice you will ever have. It will be the best decision you ever take. And so what if you stutter? People in college are way different and far more mature. it will be OK. Promise. I took a preceptorship last semester and loved every minute of it. It was amazing and I discovered things about myself that were invaluable.