"hadn't thought" vs. "didn't think"

Which is correct?

It was late and I was trying to do your package quickly and hadn't thought that I could put everything together.

or

It was late and I was trying to do your package quickly and didn't think that I could put everything together.

This is a question of 'past simple' (didn't think) vs 'past perfect' (hadn't thought). Past simple is used to indicate that something happened before the present. Past perfect is used to indicate that something happened before some other past event.

So with this specific question lets label each of the events/actions:

A - It was late

B - I was trying to do your package quickly

C - [I] didn't/hadn't think/thought that I could put everything together

If you're trying to indicate that either A or B happened after C you would use 'hadn't thought'. If you are trying to indicate that A and B each happened either before or at the same time as C you would use 'didn't think'.

Hopefully this helps if anyone else comes across this question.

In order to verify this information consult a conjugation chart for 'to think'. Check to make sure the tense of 'I thought' is 'past simple' and the tense of 'I had thought' is 'past perfect'. Do a search for 'past simple forms' and verify that the negative form of 'I thought' is 'I did not think'. Do a search for 'past perfect forms' and verify that the negative form of 'I had thought' is 'I had not thought'. At this point we know that 'I didn't think' is past simple tense and 'I hadn't thought' is past perfect tense. Now do a search for 'past simple vs. past perfect' and verify that 'past simple' is used to indicate something occurred before the present and 'past prefect' is used to indicate that something occurred before another past event. Srry I'm only allowed 2 links because I'm not a cool user.

Both are correct, but have Different meanings.

Consider:
It was late, and I was packing his items. I was going to finish it before leaving office, because I had thought everything : wrapping paper, scissors, glue & marker pens; but I had not thought of ribbons. Hence I could not finish.

Here, I was doing the thinking before packing, both in the past.

Now consider:
It was late, and I was buying things for him. I thought of everything he would need: water, sandwiches, eggs & biscuits; but I did not think of bananas. Hence I did not buy that.

Here, I was doing the thinking at the same time as the buying, both in the past.

[[ My answer is quite similar to the answer by @Kris Larson ]]