I want to return to Judaism after 25 years but I don’t really know how.

I’m a 38 year old married man with a 20 month old son. I haven’t been particularly involved in Judaism since my Bar Mitzvah and I’ve actively avoided it since 2005 due to my experiences during Hurricane Katrina and how I felt about it. Once my son was born I started to feel I should involve myself again. I never stopped believing in G-d or anything like that and to me my Judaism feels more spiritual than cultural. I don’t want to deprive my son of his heritage though so I want to start the process of returning to Judaism. My wife is a Gentile so in many ways I’m on my own in this. I found a nice reform synagogue near me and I’ve gone to Shabbat services there a few times. I sit in back and leave before anyone can approach me at the end of the service. I think it’s because I feel a large amount of shame for turning my back on G-d all those years and for some of the ways I lived my life during that time. I also have this nagging feeling like I don’t belong anymore, like I blew my chance and I wouldn’t be welcome back. Like I’m not a real Jew anymore. What am I supposed to do to become Jewish again? I feel like I only know how to be a Jewish child and not a Jewish adult. How do I move forward from here? I would appreciate any advice or suggestions I won’t be able to respond for a little while though. Thanks for reading.