Sin adverbs are provided in this article. The words listed here are commonly found along with the verb sin in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb SIN.
freely
grievously
mortally
wilfully
willfully
Hope this word list had the sin adverb you were looking for. In addition to adverbs used with sin, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.