First off, DO NOT give into the thoughts of "I may never..." As Tony says, "Take 'I can't' and everything like it out of your vocabulary. Say 'I presently struggle with...' and work on it."
You have to believe you can accomplish this, and you CAN!
Next, being that this is sort of my forte, I'd HIGHLY suggest switching in week 2 to Classic. I know, I know, the Workout Guide says Lean is to lose more weight, but it's not really. What it was developed for (this is right from Tony Horton himself) was because some of the test group balked at lifting weights 3 days per week because they "didn't want to get bulky." So they couldn't call it "Don't get bulky," and chose "Lean" and a way to market that. Also you won't get bulky doing P90X, even for a man. Women simply can't without a LOT of training for years, and some serious supplementation, because you don't have the testosterone in your body to develop big bodybuilder muscles naturally.
Truth is this: You will get FAR BETTER results with Classic, and with lifting as heavy as you can. You have to push your limits to their max on all of the workouts. If you can do more than 12 reps with a weight (except Tony's 16 rep moves) pick up something heavier. If you can do more push ups during the routine, do more. Again, like Tony says, P90X is about going past that point where you think you're done but your body has more in it.
Doing Classic also really preps you properly for Phase II. If you do Lean you miss out on Chest & Back, which is REALLY a good foundation for moving into Phase II's Chest Shoulders & Triceps.
Please feel free to shoot me a message, contact me on FB or FS, etc. if you need some additional support, have questions, etc. I believe you can do this, now you just have to believe it to and make it happen.