Hola, regresando seis años después de la pregunta original que hice. I now understand the term 'hacerse bolas' without thinking about it. In fact, for me, it always conjures up the image of a juggler 'getting mixed up' and dropping the balls one by one. I think 'to get mixed up' works well; it is 'to get confused', but emphasizes confusing one specific thing for another. For example 'I got the dates all mixed up, I thought the football match on the first and the tennis tournament was on the second, but it's the other way round'. For the specific example you give voltape, I would say 'to get cold feet', but that has more to do with fear or doubt than with confusion.