You should have applied for DSO scholarships. That will get you your STE job at DSTA pay.

Anyway, i advise you to take up the DSTA scholarship. People "downgrade" from DSTA to STE and "upgrade" from STE to DSTA. Your STE job consist of lesser engineering and design that you were led to believe. After a couple of years, and especially being a scholar, you will be pushed towards project management anyway.