Voluntary NI contributions and pension

Hello,

I am new here, very grateful for a fabulous resource, and quite probably going over old ground (I'm very much a newbie when it comes to any sort of serious financial management) for which I apologise.

That said...

I've just used the pensions caluculator at .GOV.

It tells me that I cannot increase my forecast pension payout other than by delaying claiming it.

But I have an incomplete year in my National Insurance record - 2008-9 - that I can make up with a payment now (the amount will go up in 2019, the site tells me).

Am I misunderstanding things? I thought if I made voluntary contributions it would improve my pension situation. Or will those contributions simply go towards coverage of other benefits.

I'm self-employed now, but wasn't at the time the contributions fell short.

Thank you in advance for any help you can give.