Usually in college, thaving a contract does not matter as work between friends does not need this and costs are generally shared. However, in your case you guys are not doing this as friends, which is highlighted by his inital contract. If he is paying you then you are an employee/contractor paid to do a job and as is the case in most companies what you produce remains the property of the company (or person paying) unless otherwise agreed.

Hence sort this out now before a small problem becomes a big problem :)