Advice for future work
I would advise that in any future work, you make it plain to the mentor that you lack experience in major timeline projects, not PHP which you obviously have some experience from your college projects, but simply this, projects that actually need to be used and have a deadline. This means that from the onset, s/he will plan with you the very aspects that you need to accomplish, and s/he knows where to assist you and anticipates to do so, or to assign a resource personnel to do this. As you accomplish more and more projects with someone's help on different aspects of each project that you find difficult, you will be perfecting what you already know, and complementing your experience.
Advice for this current scenario
In this particular case, you now have to do this yourself:
- List the aspects you had planned to achieve.
- Tick off all aspects you think you have covered with your work right now and explain why you think so or how s/he can verify that in your own line of thought.
- Lastly, mark all aspects you think need extensive explanation for you to begin work on them.
As a junior developer, the toughest aspects have to do with tying things together. Better choices are made when you have experience with different options of achieving any goal (like in your case connecting to the database and storing and retrieving data), it's understandable not to have a grasp of better practices straight out of college, and this is the work of experience.
This list then will give her/him a simple way to bridge the gap, it will help your superior know that s/he can trust you with part work, even though you may not have a full grasp of other aspects related to that work, which is a good aspect of team playing.
Right now, the work is to quantify what you have done, and why you think its done, then do the same for what's left and why you think it's not yet done, put it in writing, email this to her/him in good writing, then s/he will be able to understand how to assist you. I hope this helps.