Following are the last year's cutoff of JEE Main:

CRL              89.7548849+

Gen-EWS    78.2174869

OBC-NCL    74.3166557

SC                54.0128155

ST                44.3345172

PwD            0.11371730

As you can see the cutoff for SC category students was 54.01... Based on the previous years' cutoffs, you have high chances of getting qualified (based on your percentile) to appear for JEE Advanced.

To check the colleges which you may get with JEE Main percentile of 68, you can use the college predictor through the link provided below: