You can't change your bar for at least 8 weeks. Anywhere that tells you differently is wrong (unless they say longer).
I still wouldn't have recommended going to a hardresser, even if they do specialise in piercings. But it's done now.
Bathe it in salt water (1 tsp to 1 pint water) at least twice a day at first. Then after about a week you can do it only twice a day, and after about a month do it only when it needs it. This is approximate as your own healing will vary. You should put the salt water into an egg cup/shot glass and swirl it around on your tummy for about 5 mins. It helps to have a towel handy. Also, you may prefer to slightly warm the salt water, but that is optional.
If you do choose at any point in future to not wear any jewellery through the hole it may heal up. It isn't fully healed until at least a year later, but even then if you take it out for extended periods of time there is a risk it will heal over. You can get plastic bars called retainers that are practically invisible but will keep the hole open. You can't use them while you're still healing, and shouldn't use them for longer than necessary though.
And never sleep in any jewellery except the bar you are pierced with