Checking grammar

I am going to purchase a legacy gift for my son's school. I can inscribe only 3 lines with a maximum amount of characters. There is a protocal for the 1st and 2nd lines. The first line is the student's first and last name. The second line is Class of 2017. I want the last line to read: In Gratitude. I generally use With Gratitude, to send a thank you letter, but I am truly sitting in gratitude to the school.

Is In Gratitude grammatically correct for what I'm trying to express, or must I use With Gratitude? Each line has a maximum of 15 characters including spaces and punctuation.

Thank you.