The problem: People tell me I use too many big words! What can I do to sound better?
The answer: Hang around (socialize) with native speakers more—do things with them so you become accustomed to their style of speech.
Native speakers use idioms like ‘hang out’, rather than formal vocabulary like ‘socialize’.
In your question, these words [impeccable, pretentious, emblazoned] are less likely to occur in casual conversations. One reason is that casual speech leans toward words with fewer syllables; long multi-syllable words become tongue twisters if one is speaking quickly.
A person might find it quicker an easier to say ‘perfect’, instead of ‘impeccable’; ‘filled’ rather than ‘emblazoned’; pretentious is a great word to use, but a native speaker might say ‘snooty’.
A rich vocabulary is fine to have, and fine to use, but you should have more than one way to speak with people. After all, you don’t want to make others feel uneducated or less intelligent than you.
Native speakers all use the same several thousand words, and embellish with idioms, for the most part. We save those rich, multi-syllabic words like ‘emblazoned’ and ‘impeccable’ for those moments when we want to capture the attention of our listeners (and when we are confident that such words are in their vocabulary set.)
If you want to get over this big word habit of yours, do things with native speakers. Listen to how they speak about the thing you are doing together. There are many clubs, meetings, activities on. Or find a native speaker who will chat with you and give you a signal when you use a ‘snooty’ word.