Gardner timing recovery and constellation diagram
Your timing error detector should be run once for each input symbol. As you noted, your signal is far more oversampled than you need to be, so you won't end up using most of them for the purposes of timing error detection. As the paper suggests, the detector uses three samples, each separated by half the symbol period $T$. 

So, for the first timing error calculation, you would use $x[0], x[5], x[10]$, for the next you would use $x[10], x[15], x[20]$, and so on. Over time you will develop an estimate of the timing error, which you can use to select the correct sampling phase for the soft symbol decision. This will reduce your signal down to one sample per symbol, giving you a (hopefully) QPSK-looking constellation.

While you aren't using most of the samples in your signal for timing error detection, they could still be useful to you during the selection of the appropriate sampling phase. This will in general require sub-sample precision, so the increased sample rate can help you in interpolating to find the signal's value at the exact position that you want.