Money Matters

Alright so ....most of you who read this probably know that I grossly overspend in ways that I probably should keep account of. I have become horrible with money and my parents/friends have gotten on to me  about this several times. So its time to take drastic measures....I must budget. I was given 100$ in my account I am supposed to cover groceries with this money and food and (side spending). I was really proud of how well i was going to be with this money. Let me tell, you money just disappears its like a magic trick (I think its one of the best ones out there...still haven't figured out the secret). On friday I went grocery shopping and spent 35$ ( I thought that it would be enough for the next whole week). On saturday I went to a local barnes and noble to study for biostats and of course I am going to buy a cup of coffee ( WHO DOESN'T?) and on a break I might have toured the target ( I WAS REAALLY REALLY REALLY GOOD...but i gave in and bought a shirt...it was however only 6$- in my defense its one of the colors of this season). The point is I realized that I had only 46$ left in my account and I was in trouble...so I sought help. I asked one of my friends to help me keep on track and teach me to budget. On a side note: this was probably something I should have been taught at a young age (that was a fail). His response was that I should use the remainder of the money for the next two weeks and split it in half---one half would be for spending and the other half would be for shopping. Every dollar I spend from this week will be taken out from the shopping half. It was a plan. I did no spending on sunday. Today I did no spending ...and then my room-mate needed to go to wal-mart. The truth is I did forget to buy salad and salad is an essential and I thought I needed soda too. I get there with the intent of buying two packets of salad and a soda and leave spending 18$ (=( ) that leaves me 6$ to technically keep within my budget for the rest of the week. Do you think I can do it? Any tips?