If I used my RRSP as part of the HBP in March 2016, am I right in thinking that I have to insert an amount under repayment in my 2018 return, as opposed to this year?

You are correct.

HBP repayments start in the 2nd year. This year's Notice of Assesment will contain the amount due each year and all other info you'll need to start repaying.

https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/rrsps-related-plans/what-hom...