To dream of school credit represents experience or accomplishments you are building up in some area that is important to you. Having school credit reflects what you have already achieved or what you've been through.
To dream of not having enough school credits to graduate represents feelings of lacking experience or accomplishment to achieve a goal or make progress. Not having what it takes to get to the next level of your career, relationship, or lifestyle. This type of dream is common to people who secretly feel their talents or accomplishments are flukes. You may not be giving yourself enough credit for what you have achieved.