Today, the adjective hemsk means 'terrible', 'awful' or 'grim', so it has decidedly negative connotations. The noun en hemskhet means 'a horror'
You can also add a 't' use it as an adverb, hemskt, which might take some practice to pronounce correctly. As an adverb, it is similar to the English word 'terribly' and can be used as an intensifier without any negativity. For example, you could say jag är hemskt ledsen (I am terribly sorry) or filmen var hemskt bra (the film was awfully good), or vi var hemskt kära! (we were terribly in love).
Usch, vad hemskt! via GIPHY
The word has an interesting history.
It has the word hem (home) as its root, so was originally used to describe something linked to the home or connected to the home.
Then it came to refer to people who had never left home, and gradually the meaning evolved to become 'timid', 'foolish' or 'dull', and the negative meaning was further strengthened over time to the current meaning. This meaning became popularized during the 19th century, and one of the works of poet Elias Sehlstedt is titled Hemskt är lifvet (Life is ghastly).
On the other hand, if you do want to describe something as 'homey', you probably want a word like trivsam (comfortable/cosy), enkel (simple, unfussy) or hemtrevlig (just like home, cosy).
Vilken hemsk tanke
What a horrible thought
Det var en hemsk tid för oss alla
It was an awful time for all of us