Translation:My novel is badly received; I'm very disappointed.
The French often use present tense to describe past events, but in English the past tense would be used. So "was" is the correct translation - see https://www.lawlessfrench.com/grammar/historical-tenses/
It's using the passive voice which may be a construction you haven't seen before https://forum.duolingo.com/comment/30372934/TNs-U68-Verbs-Passive-Voice-Construction-Uses-Passive-PC
That's accueillie ( https://forum.duolingo.com/comment/39858861?comment_id=39858862 ) and yes, that's the feminine as participles vary with grammatical gender and number (accueillis/accueillies in the plural) after être.
I would say that "My novel is badly received; I'm very disappointed" is a poor translation. I think a better translation is "My novel is not well received; I'm very disappointed." This was not accepted as a correct solution. Reported 11/10/20 https://context.reverso.net/translation/french-english/Mon+roman+est+mal+accueilli%2C+je+suis+tr%C3%A8s+d%C3%A9%C3%A7u.