Your lawyer advised you correctly. Coram nobis does not apply here.
Kevin King, Principal- Essential Law Services. HTTP://ESSENTIALAW.COM, 415-562-6862. The information presented here is general in nature and is not intended and should not be construed as legal advice for a particular case. This post does not create any attorney-client relationship with the author of the question answered. For specific advice about your particular situation, consult with me or another qualified attorney off-site.
The law requires that the judge, before taking your plea, determine whether you understand the rights you are giving up by pleading and that your plea is freely, knowingly, voluntarily and intelligently given. You had many opportunities to express to the court that you felt you were making the plea based on finances and not actual guilt.
Of course, the court would have responded that it would appoint a public defender to represent you. You could have had this representation for free, by a highly-skilled attorney from one of the finest PD offices in the country, who gets paid the same whether the client pleads or goes to trial.
This is your life. You had an obligation to yourself to fully participate in the process by asking questions, protesting strategies, or relieving an attorney with whom you did not get along. You chose to acquiesce and blame the result on the attorney. A court will not set aside a guilty plea because of "buyer's remorse," which is really what you're describing here.
No criminal attorney that I know would advise a plea because you couldn't afford it. Public defenders are competent and you inquiry lacks what i needed for an opinion. Good luck