am worried if lrdi sets are difficult , like in some mocks , any suggestions what should i do to be confident of atleast 2 sets on d day ?

Selection is the most important thing during the exam. Even among the ones you pick- the one that requires the least time should be done first. And this selective approach is a mix of confidence & gut feeling.
If I pick a set that drains 25 mins out of 40 mins.....I don't think that I'll be able to solve any other set due to the enormous pressure.

If they are difficult, they are difficult for everyone, in that case, you should focus on being able to solve 1 or 2 sets completely even if it takes a majority of your time. Try solving really tough sets, here or somewhere else, without putting a time limit. That way, even if all sets are difficult, you can still dedicate your time to just one or two, and be confident that you can get those done reasonably well.