note: 努力 is two characters and must be written as such, regardless of whether you do them horizontally or vertically.
This might seem obvious but I have seen goofs such as someone taking the word 折紙 and writing it vertically in four pieces (so making 紙 into 糸+氏 ). This was on an actual item for sale in a store (bad package designer, no biscuit).
The layout in the original shirt is fine so best to just stick to something similar if you're not familiar with the language.