My biggest mistake working as a freelance consultant and truth be told still one of my biggest weaknesses is under estimating the the amount of work a job will require. I now tell myself any time I plan a project, whether for myself or someone else to double my estimate of the work required.
Many times it wouldn't even be my underestimating but rather the clients changing their plans halfway through and I would end up losing out rather than risking having them give me a bad review.
It is always better to estimate high then charge less than the other way around.
If you don't get a job because your too expensive don't be too upset, don't sell yourself short. IMHO it's better to not get the job than to work your fingers to the bone, miss out on other jobs and get burnt out only to go broke in the end.