How much did you pay for those 600 people and were they targeted long-tail searches from google (ndas for freelancers) or random visitors? Usually the conversion rate for visitor to payed customer is 0.1-1%, depending on your product, that's normal.
We paid nothing, it was all from Product hunt. We were on the top 5 day before yesterday.
Try targeted long tail google ads. If you spend $200 for every acquired paying customer, you are golden. Send me an email if you have questions.