I'm assuming you've had a few days of business under your belt before doing the Grand Opening event...

Check out Square Marketing. This is an extraordinarily powerful tool that is wonderful to have at your disposal. Yes, there is a monthly charge, but I posted about why it's worth it in this thread.

Once you're in, you can blast an email to everyone who has an email on file with your store and has allowed marketing messages. Additionally, you can have a marketing email show as a boosted post on Facebook to bring you that much more exposure.

Outside of Square, get a hold of your local chamber of commerce. My chamber here does ribbon cuttings and they put all of their established marketing tricks to use to bring quite a few people out to the event. If you're chummy with local elected officials (which you usually can be just by contacting them!) let them know. They may be able to make an appearance. Same with the local fire and police departments. If there are any "big names" in the community--civic leaders, citizens that are well known to have sway in the community, etc--make sure they know about your grand opening as well. Lastly, watch Twitter, Facebook, and Instagram to figure out who the big name players are for your community. If you get them on your side, they will do quite a bit of social media advertising for you.

Best of luck to you and your business! It is excruciatingly tough to run a small business in this world, but the end results can be worth it if you put your all into what you love.