It could mean that the little appreciation you've expressed is all you can summon, or that you're so filled with gratitude that you feel like you'd float if you were any more thankful. In your context, you are expressing sincere gratitude with the phrase, especially if the rest of what you communicate says likewise.

Can't be grateful enough meaning?

Meaning/Usage: To be very thankful. Explanation: This is commonly used when you feel that simply saying thank you is not enough. If someone did something very special for you, then you are expressing that no words can repay what they did.

Are thankful and grateful the same?

The Oxford Dictionary defines the word thankful as “pleased and relieved.” Both of those are great feelings. ... The Oxford Dictionary defines the word grateful as “showing an appreciation of kindness.” This is where the difference lies; being thankful is a feeling, and being grateful is an action.