You have to add two things to check your accuracy. First you should define an evaluation strategy, to regularly evaluate your model on the validation set (in TrainingArguments, add evaluation_strategy="steps" to evaluate every eval_steps steps or evaluation_strategy="epoch" to evaluate every epoch).
Then you need to add a compute_metrics function to your Trainer, see for instance in the run_glue script 48 how one is coded, that should return the accuracy you want.