There are a few reasons why your cookies might be coming out too flat. It could be that you're not using enough flour or that you're not creaming the butter and sugar together long enough. If your dough is too warm, that could also be causing your cookies to spread too much. Make sure to chill the dough in the fridge for at least 30 minutes before baking to help prevent this. Lastly, make sure you're using fresh baking powder - if it's old, it won't work either, and your cookies will be flat.