The Boost app is so horrified by this repair that it crashes every time this photo loads. Or maybe it is trying to protect me, as it reminds me of my ex-husband's work.

Like @useless_modern_god@aussie.zone says, you need to sand it back and paint over it. It's hard to fill a hole without something behind it - too late now, but put a piece of thin wood or similar inside the hole and then glue (you can use some string to pull it forward). That gives you a solid base to work on. I found the best technique for getting a smooth finish is to hold the spatula or scraper at close to a 90 degree angle and scrape off everything you can. If you hold the spatula more parallel it bends a little and won't create as flat a finish.