Hello! So usually when we use "No wonder...", we follow up with a reason. "No wonder" is used to express how you realized something that was obvious except you realized it in hindsight. For example: "No wonder my television wasn't turning on. I didn't have it plugged in!" So your use of "No wonder" feels a little bit unfinished since a native English speaker would have expected you to give a reason afterwards. I would say "I knew this sentence was wrong all along, but I didn't know which part was wrong." Hope that answers your question!