Good job letting it go. Garters aren't good to catch wild and keep unless you let them go in the fall.
Garters are cool because they roam and eat all spring and summer, then turn around and head home to get back together in big groups to hibernate. I used to catch and keep them when I was a little kid and would let them go at the end of summer because I thought it was neat that it would go home to friends and family. Probably have an interesting story to tell!
Was watching this program on garters once and the herpetologist was saying that while garters hibernate together, there are never any hatchlings mixed in. He laughed and said it would be great to be the first to find the mysterious lair of the 1st year garters. Cool, huh?