I booked cheap room and travelled back next morning as no way of getting last bus
you could contact them and ask about going from the stadium to Reus with them (take in mind that after the match there will be something for Andres Iniesta retirement and perhaps some celebration for the league title), so the bus could leave quite late.
ps: if you bought your match ticket to a reseller i hope it is a legit one or you will be kicked out (on last match vs real madrid 2800 fake tickets were found, falsified by resellers using season passes QRs, and now those QRs have been blocked so etickets sold using those QRs will not be valid).
if you rent a car and drive to Barcelona in the morning, take in mind that parking around the stadium on match days is restricted, so if you find a free spot try to read well the parking signals so you are not fined or even get your car towed.
on carrer clos i calcat there is a public parking close to the stadium and easy exit after the match. a full day pass might cost around 20-25€.