Underwhelming

Underwhelming
 

I was invited to a religious service last Sunday and later asked my opinion about it. I wrote "frankly, it was pretty underwhelming".

Later, I looked it up in dictionaries to detect whether I made a mistake or not. To my chagrin I found many stating

underwhelming = decepcionante

which I think not to be the case. To me something underwhelming is something that fails to make a good impression, not something dissapointing or frustrating. I meant to say "sinceramente, me dio una impresión bastante pobre".

Was I wrong and should I write to make amends?

No apologies needed!
English language dictionaries list underwhelming as the antonym of overwhelming.
Something underwhelming fails to impress or excite a person.

Perhaps a better translation into Spanish would be 'poco entusiasta'
('algo que no logra impresionar').

These also work:
The service didn't impress me (any/much). It failed to impress me. It wasn't very stirring/exciting.

Thank you a lot, Rusty!