Hey Riya,
If you failed in improvement exam, then you will be regarded as 'fail' in the improvement exam marksheet and can't give compartment for that (improvement exam), but it's ok...
As your original (previous) board marksheet would be still valid and taken into account for admissions to college and jobs. So, don't worry about it.
But keep your both markshhets with you as you might need to present it as when required.
All the best!