Hang in there Smarky!
Just the fact that you "caught" yourself visualizing something negative means you're on the right track.
Prepare some simple positive statements/visualizations to rescue you when you find yourself having unwanted thoughts. For example, every time you catch yourself having negative thoughts about money, visualize your bank statement with specific (high) dollar amount, and say something like, "Money flows easily into my bank account" (or whatever works for you).
Do everything you can to keep yourself flooded with happy emotions....watch funny movies, listen to upbeat music, eat healthy foods, go for a walk.
Your mind has been programmed from birth, and to re-program it may take some time and effort. You'll experience ups and downs until you start to stabilize into your "goal vibration"...baby steps.