Its not a big deal because it has no further consequenses other then paying 2000b fine the next time you do business at the immigration. don't exaggerate the issue.
Bangkok Bank has stricter requirements for opening accounts for foreigners, particularly those on tourist visas, including the Destination Thailand Visa (DTV), as it's considered a tourist visa.
You get 90 days stamped if you really applied and got a 90 days visa. You talking about 60 days stamp makes me think you applied for a 60 days tourist visa and you already include a possible exrtension to it which is not a actual visa.