Yes, it could be "at the bank" (Duolingo also accepts it). "Al banco" would be "to the bank".
I pronounced it three times and it was not accepted:( An unemployed person having issues with banks - oh, the irony!
may I wonder how to spell first letter in "banco": shoud I spell b as v or b because computer voice confuses me?
It is always spelled with a 'b'.
In Spanish, 'b' and 'v' are sometimes pronounced more like an English 'b' (e.g. boleto, viernes), especially at the beginning of words. In other cases, they are pronounced more like a sound between an English 'b' and an English 'v' (e.g. jueves, escribes).
I just got marked wrong for saying "on the bank" since it also means a river bank, and it should be accepted.