I'm the treasurer of our stokvel and I'm worried that the numbers don't add up.

We are 12 at our stokvel, 3 years running, R2000 a month each. I took over as treasurer in January because nobody else wanted the admin. Last week I sat with the spreadsheet until 1am and there's a gap I can't explain, its not huge, but about R6400, but it's not nothing and it's not adding up to a typing error I can find. I haven't told the group yet. I keep re-checking because the alternative is me telling the 11 women I've known for years that either I've made a mistake with their money or someone else has. Not sure how to approach this.