Attending a few classes won't kill you. At least keep a good record of attendance. If you are currently on ED and didn't attend class. Be prepared to get rejected without reason as the previous ED itself is a red flag. Read here and you can see many ppl got rejected with perfect documents so it's totally discretionary by the embassy and they like to presume guilt unless you prove yourself otherwise. I got rejected the first time with well over more than 1Mthb in my account and a 6mo course. Everything was authentic and well organised. I had multiple visa exemptions and previous ED as well.