I'm writing my first book and I have set my goal for 70k words. I'm almost done and have only accomplished 45k. Does anyone know what is the standard word count for a romance and should I try to fill in my book?
The largest romance publisher has a number of series that target 50k word novels: https://harlequin.submittable.com/submit Personally, when I listen to a CD and hear a cruddy filler song, I skip it. When I'm reading a book and realize I'm reading filler material, I get distracted from it and never find it again. There are lots of short books I love.
The only acceptable filler is the kind that is way more interesting and has little to do with the rest of the narrative. Sadly no one has figured this out yet, and just like to do something I equate to shooting a chunk of the film aimed at random things that are kinda more background, and the cast is out back having a smoke break. The best answer is filler is bad, filler is fluff, and fluff is for cushions and not for stories. So say to thyself: "I am writing a book, not making a throw pillow."
I understand how you feel, your book just doesn't feel as "serious" as it should unless it's about 500 pages. But I can assure you, as long as you put your heart into your story and treat it with respect, regardless of how short or long it is, it will be a good story. Even if it's "short", there are countless short stories that are bigger than most "long" stories in popular culture. Don't concern yourself with whatever falsified "standards" people have made up for books. Ultimately, they don't exist, and in fact the most famous books to exist have entirely broken any of these pretentious "standards" that publishers attempt to set forth.
"Bridges of Madison County" is 35,954 words. But it's awesome. It will be very difficult to get anything below 50k out. Nicholas Sparks' "The Notebook" was 52,ooo and was an instant classic. There aren't many like him, though. Harlequin (the publisher) has strict guidelines and you'll need to read a few of their books in order to get the idea of what they expect to be in a book they'd acquire. For everybody else it will be better to "fill up" to those 70k and there are different ways to "fill up". You can make it literary and add beautiful words, or you can add more plot (or sideplot). You can also take time to read a few novels in the same genre and see what they have and you don't.
If you're writing for a specific line at a category publisher you should probably have that in mind from the start - the requirements for most of them are VERY specific. So you're probably writing for a more general audience in which case, yes, you're probably a bit short. But if you haven't finished your first draft yet, don't assume your length now is going to be your final length. When I read over my work or respond to beta feedback I often add up adding extra scenes, etc. You may find you're in the same situation.
45k words sounds fine to me, but I am no expert on US publishers. As to what to fill your novel up with, here is one idea: write scenes into the novel's initial part that explain more thoroughly how this or that came to happen. In other words, read your novel and look for places where the reader might wonder: how did so-and-so end up in this situation/state? And then write an earlier scene that shows how they did.