There's no refund of any portion of your $2,800 MA top up unless you exceed the CPF Annual Limit in 2020.
You're not going to hit the CPF Annual Limit via compulsory contributions that soon even if you do hit it in 2020. Let's assume you're earning at least $6,000 per month in regular salary for all 12 months in 2020. If that's so, and if your variable pay (bonuses, commissions, 13th month, etc.) totals $22,432 or less, you should have enough room below the CPF Annual Limit to squeeze in your entire $2,800 top up.