I was baptised a month ago, but I didn't attend a class for it, is my situation usual ? I‘m worry about it.
In some churches, yes it is unusual but not in all. It is VERY important for you to either talk to the rector of that church about education in Christianity or read avidly the books that others here will recommend. @Liturgyworks @anglican74 @Stalwart. My suggestion would be C.S. Lewis' "Mere Christianity" and of course the Bible, esp. the Gospels.
The Book of Acts records some baptisms, but makes no mention of the baptized attending a class beforehand. I think you're ok. But now, as Brigid has pointed out, you do want to grow in your faith and knowledge of our Lord and learn how to discern His will for your life. The Bible is our guidebook, so I hope you'll start reading it (if you haven't already). Luke's and John's Gospels, the Acts of the Apostles, and Paul's first letter to the Corinthians would be great for starters. Eventually, reading through the entire Bible (it doesn't all have to be read in order) should be a top goal of every Christian IMO.
Nope, unless it wasn't in the name of the Trinity, Father, Son and Holy Spirit. Only one baptism (in the correct form).
Thats correct. If perfect faith or perfect knowlege were required to be baptized, either no one (but perhaps the very arrogant) would be. Or, as some credo-baptists do, we would be re-baptizing constantly.
Any baptism in the name of the Father and the Son and the Holy Ghost is valid and permanent. You're good.
Thanks, I have a last question, I know it sounds stupid, but I still want to make sure, do Anglican use the Trinitarian formula for baptism?
Absolutely we do. All it means is that the baptism is made in the name of the Father, the Son, and the Holy Ghost. Pretty much all "mainstream" Christian denominations will baptise like this.