Well, you have not pointed out what exact problem are you facing ? Are you having timing issues or is your accuracy low ? How long have you prepared and what has your preparation strategy been like ?How good are your concepts ?
Regarding your point that if you're given more time, you'll have better chances of getting a question correct. I think that's quite usual. I think if given more time ,most of the candidates will probably end up solving most of the questions.
The fact that you're not able to solve the questions in a short time in a particular area may indicate that your concepts in that area are weaker than you think them to be. Maybe you should do some more work on the various topics and see if there are some better approaches to doing questions.