The contributions paid by you and your employer are not directly linked to how your benefits are calculated. They are there to ensure there is enough to fund your retirement.
In alpha, you accrue 2.32% of your earnings each year as annual pension. If you had pensionable earnings of £25,000 in one scheme year, you would accrue £580 worth of pension. The contributions you paid in this year would be £1,150. The £580 pension earned will be paid to you every year in retirement. This means, less than two years into retirement you’ll already have received back every penny you paid in contributions. The rest of your pension is financed by the employer contributions paid. More details can be found in the alpha scheme guide.