If i contribute more money towards the HBP contribution. Does that decreases the amount i have to pay next year?

Yes. You can contribute extra every year to reduce future payments’ amounts. For example; if you withdraw the full $35,000 and paid $4,000 in the first year, the next 14 payments will be reduced to: ($35,000 – $4,000) / 14 = $2,214.29.