Interpreting random seed effect on correlation in regression with small sample
This means that your model is not consistent. Your problem is hard because of the small sample size. I would recommend reducing the number of predictor variables.

7 predictors is quite a few for linear regression, even with a large sample size. Try and get the best results you can with 2 or 3 predictors.

If you can predict with 30% accurately all of the time it is better than 70% accuracy 10% of the time.