First Trade Problem

I finally pulled the trigger on my first trade using the 15 min scalping system with some interesting happenings.  I'm concentrating more on observing my own behaviour with each trade and understand the motivation behind my actions.  

Looking at the chart below the set up was exactly what i was hoping for. That is a buy signal at the low of the day and right at predefined support.  Entering that trade was made with very little hesitation.  Although whenever I place a trade it always crosses my mind it the trade will go against me which is a normal reaction but i found comfort in that I define my loss not the market.

The broken line is the intraday support and resistance line I discovered after I placed the trade at 210.90 so I had space for a decent 20-25% gain so long as I stuck with the plan.  That plan was to hold if and when the SPYhit 210.90.  Sell half the position and wait and see if a breakout ensued.  What did I do?  Sold the whole position after it hit 210.90 (@1pm) and dropped back for a 11% gain.  That bothered me because I didn't stick to my plan (which cost me an additional 10%).  I think it was my fear of trading a new system for the first time and felt the need to prove myself right no matter how small the gain.  But I felt more like a failure not following the rules.  I'm hoping I get better at that as I continue to trade the system.

Here are the trades.

BOUGHT 5 SPY Mar06'15 210.5 CALL @AMEX @ 0.95 
SOLD 5 SPY Mar06'15 210.5 CALL @AMEX @ 1.05