I don’t think St. Peter is going to turn people away at the pearly gates for being over-baptized.
Baptism is an outward sign of an inward change. A public declaration for your choice to follow Christ. I would say that being baptized before you make that decision would be less meaningful than getting baptized intentionally after you made the decision.
If a church you are going to is telling you your baptism wasn’t good enough because it wasn’t “their” baptism it should send up some warning signals. If you were baptized in the name of the Father, the Son, and the Holy Spirit at any point in your life, you’ve been baptized. Period. As Christians we confess ONE baptism for the forgiveness of sins. People telling Christians that they need to be “baptized again” (technically impossible anyway) really upsets me.
A Vatican Swiss guard stands during a meeting between Pope Benedict XVI and the Armenian president, Serzh Sargsyan (via guardian.co.uk)