Your interest rate could fluctuate either up or down. This can affect your repayments. If the interest rate goes up, your repayments will also increase, if the interest rate falls, your repayments will also go down.
Your interest rate is fixed at the time you settle your loan for a term of 1 to 5 years. Fixing your rate means you will know what your repayments will be and they are unaffected by interest rate changes during the fixed period.