Need Wood Engraving Help

Hey everyone,

I'm attempting to engrave a decent sized sign for my wife out of 1/2" Ambrosia Maple. As I started cutting I noticed my engraving wasn't consistent across the piece. In some areas it doesn't cut at all.

Upon further inspection there are a few low areas on my panel. It's minimal, but it really makes a difference when my engraving isn't very deep.

Off the top of my head I was thinking a surfacing pass would have solved this. But is that common when engraving a wood sign? Any tips would be appreciated. Also if theres a way I can save the panel and try again I'm all ears because I'd rather not have to mill and glue up a new one.

Here's a picture showing what I'm talking about. It's still running the job.

Thanks in advance!