If you are unable to complete your levels in a week:
Are you still using the Legacy Editor?
If yes, get 2.0, which has PGE, because you are behind the times. PGE is a more efficient engine to make your levels, so you will automatically get faster at building levels
How well does your PC perform?
The slower your PC the slower your editor (hopefully PGE now) will load. The slower your editor loads the longer it takes for you to finish you level. If this prevents you from finishing it in one week, once again, you are behind the times. Upgrade your PC or buy a new one.
If after both of these you still cannot complete your level in a week, you are an inherenty bad level designer. Ask good level designers for advice to get better. Heck,try to complete your levels in less time. The better a level is, the less time it took to finish it. The best contest levels were started literally the day before the deadline, like this awsome masterpiece