Proper assignations of current directions
No, the result won't be wrong. If you would have chosen the wrong direction the result will be negative, that's all.  

It's not always easy to know in advance what direction the current will flow. Don't worry about it, just choose an arbitrary direction. Just make sure that you document your choice by drawing an arrow next to each branch.



As a matter of fact, when you solve the problem with the assumed current directions you'll find that one of the currents is negative, so its direction was assumed wrong.