When I type よかった (yokatta) in romanji, the small つ (tsu) becomes the "tta" sound.
The "t" became repeated so it somewhat sounds like a small つ (tsu).
For example, まっちゃ (matcha). "Matcha" is the romanji, but if I was writing out the actual word for word, it would be something like "Ma cha" and the purpose of the small つ is lost.
For something like, かっこい (kakkoi) the "k" is repeated.
Well, the point is to get the small つ sound in English haha
Dunno, hope this helps?