"Make every effort to enter through the narrow door, because many, I tell you, will try to enter and will not be able to." (NIV)
Strive to enter by the narrow door [force yourselves through it], for many, I tell you, will try to enter and will not be able. (AMP)
Strive to enter in at the strait gate: for many, I say unto you, will seek to enter in, and shall not be able. (KJV)