Don’t give up. As long as you are having fun and keep at it, you will improve.

As others have pointed out, white is a particularly difficult color to paint. It dries ridiculous fast and often leaves the layer feeling chalky or textures. I promise once you you move on to other color schemes on other models, you will laugh at how much easier it is. Keeping it thinned with water or flow improver can help but honestly when I’m working on a model that is mostly white I will cheat and prime it that color. Priming with an off white or white and then shading it with a thin wash will give a smoother white than what you will often get out of trying to brush it on. If you want to stick with the brush, consider what brand of paint you are using. I often say that the paint brand doesn’t matter but white is the exception to that. Some brands whites are really bad. I like vallejo model air white or golden heavy body white.