本人已35歲想移民到美國，但因20歲時誤交損友，有遊蕩罪案底，當時無入獄，只是入了勞教中心2個多月，會因此而移民唔到去美國嗎？

有遊蕩罪這個罪嗎？
最多只是違反社會秩序維護法而已

It is always a possibility.

However, given that loitering is not a criminal offense in the U.S., based on the circumstance of your incident (per police report and court filing), it is possible that your criminal history will be forgiven for immigration purpose.

At this moment, it is difficult to tell how exactly your impact will be.