If you haven't booked your accommodations yet, I would recommend booking a room at the Hotel del Rey. It's the place you want to be if you're new to the scene, because you're quite literally in the middle of all the action. The world famous Blue Marlin Bar is right down in the lobby, and meeting women there for fun times is like shooting fish in a barrel. And since you're in town for just a short time, you won't want to be wandering around lost trying to acclimate. Just to let you know, the del Rey is a nice hotel, but it's no five star digs. Expect about what you would find at a decent three star hotel in the United States. Save the luxury accommodations for later trips, because the luxury properties tend to be located a bit outside of the areas of main attraction.:
http://delreyhotel.com/Next, I'd recommend you stay two nights instead of just one. You'll be having such a blast that you'll regret it if you arrive in San Jose and find you have to leave the very next morning.
Sorry you got scammed in Jaco, but there's a bit more oversight of the scene at the del Rey. It's far from perfect by any stretch of the imagination, but it's better than nothing. If you are scammed, report it to the hotel staff. They don't like scam artists on the property because it's bad for business.
You can meet women who will spend a day or more with you in Costa Rica, but it's far more common to find that situation in places like Thailand where a woman will spend weeks on end with you if you really hit it off with her. Best of luck on this front, but you might discover finding such a situation to be a challenge in the short time you have available to you.
Most of all, relax and have fun! You'll meet plenty of guys at the Blue Marlin who will be happy to serve as your wing man just because they like to introduce others to the scene and make sure they have a good time on their maiden voyage. So don't worry about being a newbie. You'll find yourself fitting in quickly.