A wise man once said "If you ain't fucking something up you ain't getting nothing done" It's a double negative but I don't think he intended the reverse word play.
Anyway, when we make the decision to maintain /repair /modify our own cars there's always things that go wrong. We learn from those mistakes and it's how we become competent.
Everyone here has had things go wrong and made things worse with a novice repair several times over in the beginning.
If you keep trying then things get easier, and yes that shop sounds much too costly.