Income tax

Hi,

Recently became self employed and struggling to understand the tax element. I had been quoted £436 for my tax payment, as I've just come out of my personal allowance. However, I earned £1082 last week and recorded this income on my app, only to be quoted £869 for my projected tax payment. 

This has jumped £433. This would be around the 40% deduction, but I haven't reached that yet and should still be in the 20% bracket? Confused as to how this calculated. I earn roughly the same every week. Surely 433 every week is excessive?

Any advice appreciated.