Coming Back To The Church

I was raised Catholic, but left in my early 20's for a non-denominational Church.  I now realize that this was a mistake and I want to come back.  I was baptized, received first Communion and Confirmed.  Do I have to go to classes or do some special process to return to Mass?

Well first, praised be to God that you want to return. Anyone is always welcomed to come to a Catholc Mass, regardless of their religion. I am assuming that your question is that you want to participate fully in the life of the Church again and receive the Eucharist.

As long as you have not done something to incur ex-communication (such as having procured multiple abortions), all that is required is for you to make a good Confession. You do not have to go to class or take any instruction whatsoever. If you have been ex-communicatied, you may require a meeting with the local Bishop

You did not state how old you are now or how long it had been since you made a good confession. If it has been many years, you may want to make an appointment to see a priest for Confession rather than wait in line on a Saturday or a Sunday.