Made a mistake and filed 7 allowances on w4. I only have 2 dependents. No federal taxes were taken out for half this year. Just changed this to 3. How wll this affect me?

I only make 25,000 a year. I am concerned I will end up owing, or not get a refund at all being that I just changed the allowances from 7 to 3 and we are now in august with only 3 months left of the year, assuming they will start taking aome dederal taxes out now once HR process this.