Hi. In your sentence, I believe it needs to be corrected as either of the following: I " felt" very embarrassed at such a careless delay from my side as I had completed work on the first draft well within the scheduled time. or I feel very embarrassed at such a careless delay from my side as I "have" completed work on the first draft well within the scheduled time. I explain in terms of grammar: the past perfect tense (e.g. I had eaten) can only be used in a sentence where the phase of past sentence is used. Similarly, present perfect tense can be used in a sentence of present tense. I hope this helps!

hmm...good tips from the guys, but it looks a bit wordy to me. maybe try "I was very embarrassed by my carelessness (in what?) although I had already completed my first draft well within the scheduled time." but you should explain, carelessness in what? a trick to improving english is to be concise yet specific although there are so many ways to capture the same idea/s.

of course you can but you should know is the sentence in which tense.