If you are paying attention to your breath, your mindfulness practice is working for you. Feeling sad, angry, scared, or nervous is not a sign that your practice is not working. It is a sign that you should check in with your breath and continue practicing. Noticing that you are having these feelings is a sign that your practice is working. Without a mindfulness practice, you could carry these distressing feelings for a long time, trying not to notice them, or imagining that they are embedded in your circumstances. If you are able to recognize a feeling and breathe consciously with the feeling, your practice is working well.
Practicing mindfulness works whenever you practice and it has a cumulative effect the more you practice. The end goal is not to stop feeling sad, scared, angry or nervous. The end goal is to feel what you are feeling when you feel it. The end goal is always being present, and engaging with what the present moment brings you.
As you practice engaging with each emotion as it arises, you will increase your resiliency. You will return to a baseline state of calm more quickly. Your baseline state of calm may also become more calm. Those are not the goals, those are the outcomes. The goal is always to be present where you are. Whenever you are present with your thoughts and feelings, breathing with awareness, evoking compassion, your practice is working beautifully.