Mahi doesn’t return to the college after her summer internship and everyone blames her classmate Abhinav who used to stalk her for her drop out, so guilt ridden Abhinav takes a journey to convince Mahi not to drop out because of him, but in this journey he discovers darker and shocking secrets of Mahi.

No need to mention the character names in the logline, best to describe them instead. I suggest you read the 'Formula' tabon the top bar to learn how loglines are structured.

A few helpful tips to get you started:

Describe one MC it sounds like the guy (Abhinav) is your MC focus the logline on his POV, in other words, what events motivate him and what he must do to achieve his goal.

If you describe him as a stalker, it will be very hard to raise the audience empathy for him.

Getting Mahi to come back to school seems rather lack luster a goal. What else does he do and what is his objective goal?

Rather than using names use an adjective to define the protagonist that adds to the difficulty of reaching the goal.
Hope it Helps

Sounds like an interesting concept.
Just be sure to know how to write a logline. What you've written above reads more like a story summary in a tv magazine.
Use the following formula and try it again:

When?[a major event happens],?[the hero],?must?[do the main action].

Also, you don't need any specific names or long sentences inside the logline.
Be sure to state a clear objective goal your hero has to achieve by the end of the story. "Discover dark and shocking secrets" sounds too vague for me to create a concept for a feature-length movie.