If you've never done a budget or spending plan before, you're not alone. About half of Americans don't have a budget. But knowing how you spend your money is an important step in deciding how much you can afford to spend on a home. Even if you don't generally like to think about money, it's doable. It's worth it to spend some time looking at your spending now, as you're deciding how much you can afford to buy. Research shows that people who plan carefully for big purchases like a home are much less likely to have financial trouble later.
Don't edit your budget to reflect what you "could" or "should" be spending. The goal here is to assess what you are spending-in the next step you'll decide what changes you might be able to make in the future.