'I am totally beside' does not make sense, as it does not stand alone, 'beside' indicates the relationship between two things. Therefore none of your options are correct. You are correct that there is an expression 'I am beside myself' but 'myself' cannot be omitted as your test has done. If the 'myself' is included then the correct option is 1.

This makes no sense. There are many bad English practice books. This could be one of the bad ones.