Buy the book “Financial Modeling” by Simon Benninga. Deal Maven, Wall Street Prep, Kesdee, Euromoney all had modeling courses. Modeling isn’t that difficult, it’s just finance and excel. If you can understand finance formulae and excel you can model. Also youtube and www.bionicturtle.com have modeling tutorials.
U have to use circular referencing in certain models. Not sure what errors u are speaking of. I did financial modeling for a big wall street bank when I was a research analyst, I’ve built models when I was in investment banking, I’ve built models for project financing as well as used excel to build my current company’s value at risk model. Benninga’s book is excellent.
There are also specific books u can get for whatever type of model u need to build, whether it’s M&A or corporate finance or forecasting or risk management.