I was advised to buy back six years at £800+ each, as doing so would lift my pension by about £50 a week. If memory serves I will have to live to 72 or 73 to break even but will then be in profit.
These things are always a gamble, but remember that pensions go up every year so what might seem like a small increase now will rise over time unless that changes.
Is the £285 for part of a year? If so, if you don’t pay it you will lose the £600 or so you have paid, as only full years count. On balance I would pay unless doing so would cause hardship.