Hi, do you know how can I get experiences? I'm on my last level where I…

Hi, do you know how can I get experiences? I'm on my last level where I should build a train station but I forgot to upgrade it instead I upgraded all the useless stuff on luxuries. I have only 51 left and need 29 xp and now there are no more side quests and I can't gain experiences to build train station. If I play the sandbox version, will I gain experience in my actual game? Been addicted to this game for days and this is the first thing I do after work, so would love to finished it before I see red! :o Many many thanks for any answers!