How much dialogue?
I've heard that as a (very, very) general rule of thumb, about one third of a novel should be dialogue. Although it varies according to genre - romance might have more, action less.
While such generalisations may seem ludicrous given the plethora of factors we need to consider when writing, to test the theorem I've looked through a few novels that I like, and they all roughly conform to it.
It seems that as readers most of us have expectations for the 'feel' of a story, its balance in the way it unfolds. Dialogue supplies the personal, living, direct connection component that keeps it moving along, while narrative provides us with "need to know" information, and description gives us "nice to know" flourishes that add richness.
At least, Julie, if you have erred on the side of too much dialogue, you are unusual. One of the commonest mistakes of beginning writers is the tendency to overwrite narrative and description at the expense of dialogue, presumably in an attempt to be literary or poetic. I call it the 'trembling leaf' syndrome, because a perfectly ordinary tree that plays no part in the book may be given its own page to be a 'dew-dripping, slippery-barked, silent sentinel of the night, looking down on the voles that frolic in furry ignorance of their incipient fate at the claws of the wise and watchful owl that calls it home'.
I've noticed that when I flick through a book I instinctively react to the shape of the text on the page. When I see nothing but ink for page after page I think 'Warning - Trembling Leaf', and long to see some white space. Like music, written prose needs rhythm, and pauses.
On the other hand, one of the dangers of too much dialogue is that it can have a ping-pong effect as ideas are batted back and forth. If something is important enough to be said, it is sometimes important to incorporate how it is said - with appropriate facial expressions, actions, reactions etc (rationing your adverbs) - the walk and chew gum syndrome.
I think Jim McD's suggestion is an excellent one. Looking at printed copy from a distance gives you a proper perspective on the shape of your text. Then you can make it more appealing (and buyable) by reshaping it to reduce or break up the forbidding density of too much narrative, and by adding texture to your dialogue to make it more meaningful and 'felt'.