Certain folks in certain regions and of a certain age group tend to use 'lovely' rather than 'beautiful' in certain circumstances. I am of that ilk. So far, I have yet to see my use of 'lovely' (rather than 'beautiful') marked wrong in connection with my Esperanto lessons ... when I use it correctly in my dialect of English.
I'm surprised to find out that you had 'lovely' marked wrong for this sentence. Although I used 'beautiful' in this instance, 'lovely' would've been perfectly valid in my dialect of English.
In my opinion, during these early stages of learning Esperanto, the English sentences being translated into Esperanto are NOT VERY nuanced at all ... and for good reason: Ni estas nur komencantoj. (We are merely beginners.)
Generally, "bela" translates as "beautiful". In English, "cute" can sometimes work in place of "beautiful", but not always. Like you would probably never say that a sunset is cute, but certainly could say it is beautiful. I've seen "cute" translated as "beleta", and I think that well takes into consideration the diminutive connotation of "cute".