I'm in a very similar situation. I'm a Junior Economics major who got into web development last year. Basically, a friend and I had an idea for a project we wanted to build, and we just decided to start building it up from the basics. We looked up resources as we went, and I got a good grasp of HTML/CSS and even some PHP from it. This led to us getting asked to work on a project for one of the professors here, and those two projects helped me land a web development internship for the summer.
The amount of resources that are online and all around you is enormous. I would say just keep kicking around ideas and try to put a few of them into practice. I've always found that learning through doing is the best way to learn, at least for me. In addition, ask your professors if there's anything that they could possibly benefit from having technology-wise. You might find an interesting way to combine your economics knowledge with your web development aspirations.
Just keep making stuff! You never know what could come of something until you try. If you have some time after you graduate, use it to try a bunch of different projects. Set a deadline for a very basic version of your idea, code it, test it out, get some feedback from people and just see where it goes.
