What the teacher wants depends on the wording of the question - you need to go and read this carefully.
There are complementary strands and reverse-complementary strands.
The complementary is one where you have the sequence kind of reflected - the exact complement of the top strand. In the example below, the top strand is TTCCAAG, the complement is the one below that, and you would read it in the 3' to 5' direction.
5' TTCCAAG 3' 3' AAGGTTC 5'
The reverse complement is similar, but the way you read them is, as you should, from 5' to 3'. In the example below you can see the difference - note the top two are the same as in the example above, the 3rd one is the reverse complement of the first strand, and is the equivalent of mRNA if the first strand is DNA:
5' TTCCAAG 3' 3' AAGGTTC 5' 5' CTTGGAA 3'