20% conversion rate sounds okay - but it's all relative. You'd need to know the conversion rates of your competition to really understand whether you're doing well.
Are you talking to the 80% that don't convert, to find out why?
As well as worrying about conversion rate, I'd suggest you look at the price of your product. $10 a month is nothing for a B2B product. If you product is good and delivers significant value, you may find that you're pricing is too cheap, leading to fewer sales and lost opportunity (leaving money on the table).