You can choose to start making repayments to your HBP early. If you choose to start your repayments earlier, your repayment period will stay the same, but any repayments made before you are required to start your repayments will reduce the amount you have to repay for the first year.
You cannot carry forward your RRSP Contribution made this year and designate it as a repayment in the following year, but you can still use it as a contribution on this year's tax return.
More information on repaying your HBP can be found here: How to repay the funds withdrawn from RRSP(s) under the Home Buyers’ Plan (HBP)