Small wheat powder is wheat flour, or flour.
This word uses the kun'yomi readings of all three kanji. The 小 and the 粉 both use kun'yomi that you haven't learned yet, but luckily they are both the same! Just think about how "small" things are like "children" (子), and "powder" is also small. So both 小 and 粉 are read こ.
Add three times more flour than water.
This is a sweet that is made by kneading flour.
Oh no. I left the expensive flour I just bought on the train.