What was the consumption of 0,1 M NaOH by titrating the 25 ml of the acid. The 250 ml dilution doesn't matter. This consumption gives the mole of NaOH, and calculated with the 1 protonic acid volume its molarity. Was 0,101 M your result? The make up was 59,5g/l.
With n= m/M you can calculate M = m/n
But where did you do the 1:10 dilution. This has to be done before you add 25 ml in the erlenmeyer.
Normally a measured flask has to be taken. 25 ml in 250 ml accurate. Then from this 25 ml are taken for titration.