Totally fair. I only started paying attention after hearing a podcast about how the letter “D” is pronounced in names in some other cultures. I was doing it wrong. It was a similar issue with position of the tongue when saying words like “dentist” compared to “dog”.

Reading differences in pronunciation can be difficult, but in regard to tongue placement when saying these words, when saying “blush”, the tip of the tongue should press against the inside of the top-front teeth. When saying “brush”, the tongue should curl back and lightly press on the inside right and left side of the back teeth.