You're close, but not quite right. So you're probably heard to use FOIL on a problem like this.
First, you multiply x by 3x to get 3x^2.
The outside terms multiple to give you 5x, not 3x, so I think that was your only problem.
The insides give you -6x.
The last terms give you -10.
Combine these to get 3x^2 + 5x - 6x - 10. Adding like terms gives you 3x^2 - x - 10.
Hope this helps, and have a happy New Year as well!