Go back to the shop and buy yourself (if you haven't already done so) a tutor book. Whilst you're there, ask them if they have a list of instrumental teachers or if they (as these places usually do) have a place where teachers are allowed to post their ads. Lessons may seem a little extravagent, but even if you can only afford a few, they're invaluable in the beginning. They're probably the only way you'll know how to correct what you're doing wrong.
That said, most instruments make horrific sounds when you're a beginner to them, the exception probably being the harp. Part of the experience of learning is developing the right mental attitude and the perseverance to carry on when that seems impossible.
Stick at it, and good luck.