I attended some outreach workshops by USCIS in Phoenix. The message that I got was that "Use the Best Evidence". If you do not have anything directly on June 15, think of anything that you did before June 15 and after June 15. I am not sure what you meant by "testing on the 18th", but if you have evidence of that, that's great. Be sure that your name is on the document and the document is dated. Now, think of things that you did before June 15. Also, don't give up on June 15 so quickly either. Go through your cell phone / school record / work record and check everything. When I took part in some volunteer workshops, I saw a wide range of documents, such as phone records, parking tickets, credit card payment, medical appointments records, etc. As long as your name is on it, and you have to be physically in the US to take part in it, it should be helpful. A grocery receipt that does not bear your name may not be so helpful. However, a prescription filled for your with your name might be. Organize everything in the best way possible -- easy to follow, use highlighter, tabs, etc. Make the job easy for the examiner. Seek legal advice -- whether by attending a workshop in your local area or work with an immigration lawyer. Remember, the "Wrong Help Can Hurt", so be careful of scammers. But BEST of luck.
Yes, any will help, some more than others, though. Make sure to get expert advice, don't file for DACA alone!
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.