You are correct! If your case was dismissed, and a not guilty plea was entered then there is no conviction.
You have to remember however, just because you're case was dismissed and there's no conviction does not mean there is no arrest record. If you want to clean up your arrest record for that arrest as well you need to hire an attorney in order to do so.
That you were arrested for the crime, that you were charged, and that the case was dismissed will remain on your record for life. However, since criminal charges were filed against you and then later had your case dismissed, you are in the unique position to petition for an order to seal records of the arrest and delete them completely, upon a finding of factual innocence. The petition must be made within two years. A declaration of innocence is the only way to get even the record of arrest removed from your record. You should consult an attorney to see if you are eligible. It is time-limited, and is the only way to have a totally "clean" record for the future.
Another important factor not mentioned above is the reason that the case was dismissed. Was the case dismissed because you completed the deferred entry of judgment program or Proposition 36 program. Depending on which program you completed, that will dictate the extent to which your case was dismissed. The difference between Prop. 36 and DEJ is for another topic and probably easier explained in a consultation with all the information available.