The phrase "a bit resentful" is correct and usable in written English.
It can be used to describe a slight feeling of bitterness or indignation towards someone or something.
Example: "After hearing the news, she felt a bit resentful towards her colleague for taking credit for her work."
Alternatives: "somewhat bitter" or "slightly annoyed".
While thrilled with the change, he is also a bit resentful.
Then I think some people became a bit resentful and started saying that it's not their fault it was mine.
At the moment, students from abroad feel a bit resentful that they are paying two or three times as much as home students.
"But I am feeling a bit resentful about having this taken away — if I can't have access to a drug that would extend my life".
Once, actresses might have felt a bit resentful that they were losing out on great Shakespearean roles here, but the all-female Julius Caesar at the Donmar should ease that resentment considerably.
I wondered if she was a bit resentful about all the time that Layla spent with the Silk family, or perhaps she is just a bit cross with Layla's father because he spends so much time philosophising.
Could they have been -- well, just a tiny bit jealous, just a tiny bit resentful that the girl-about-town had had the hubris to move from me-and-my-dating-disasters to middle-aged male Hollywood narrator and to do it bloody well?
Can't I be even a teeny bit resentful that I do all these good deeds, behave in all the right ways, and God (whatever and whoever that is) didn't see fit to save my son's life?
Reading On, After Harry Potter The truth now: aren't librarians just the teensiest bit resentful of the Harry Potter craze?
You feel burdened by this, a bit (or very) resentful and taken advantage of time and time again.
The child will probably be a bit angry and resentful.
