I have the feeling we are moving way to fast

A couple of months ago my company started a new software project. At the beginning I felt very well and I had the feeling that we were all carefully planning our steps to geht things right from the start. But since a couple of weeks I feel like we are rushing things and that we progress in an unsustainable way. Is this just a feeling that comes up sometimes? Maybe because of the agile methodology. Or is this a warning sign I should mention to the team?

Edit: To get a little more concrete: It is a webapplication in a b2b context. At the beginning we put a lot of efford into getting the concepts right, for example we worked on a localization implementation and I beleive it to be of a very good quality, same for Navigation eg., but since we start to implement the actual business logic, I feel that we are really rushing things and try to produce some value very fast whithout really paying attention to quality.