You have to start over and learn important topics and strategies involving number properties, fractions, decimals and percents, equations, inequalities and VICs, word translations, geometry. Once you are done learning or relearning, practice more under timed conditions. I would alarm you on retaking GRE in December, since you may hit under 160. IMO, four to six months of regular preparation using question banks of Magoosh and/or this forum could help you potentially achieve your target score in GRE quantitative part.