Serissa is a notoriously fickle species, but can still be great as bonsai. Generally potting soil such as what you are using are avoided in bonsai, generally a looser, more inorganic mix is used. Check out the some of the articles in the learning library forum for a more detailed description of bonsai potting mixes.
I don't have any personal experience with serissa, but according to [url=https://www.bonsai-bci.com/species/serissa.html]this[/url] article, leaf drop is common and it should grow back. Just remember that a tree with no leaves will not need as much water, and remember that some of the watering instructions on this site and others will assume a free draining potting mix. Most of them emphasize not watering on a schedule and watering based on the needs of the tree and the dryness of the soil. I think every 3rd or 4th day would be overwatering for an indoor tree with a very organic potting mix.
Also if the nighttime temperatures in your area are consistently above 50F, I would try to get your tree outside, preferably somewhere where it can get morning sun, but will be protected from afternoon sun.