Good for you!
Mounce is excellent, that is what we used in my Seminary for first year Greek. Stick with it. Make vocabulary cards and also get the CD and listen to the pronunciations a LOT. When you are driving, when you are walking, etc. Really learn the language like you are going to speak it, and it will mean a lot more to you.
When you have finished Mounce, a good bridging text is A Summer Greek Reader, by Goodrich and Diewert, which goes through the Biblical texts, and adds a lot of vocab. as well as putting the translations into simple English.
If you have trouble, you might want to access a seminary and see if you can audit courses. A lot of people have issues with noun cases and the extensive verb charts. Participles was my nemesis, I had never studied them in any other language. I did figure it out, though! If you build slowly, you should be ok. I love Greek!