I rebuilt one of those pieces of #@&!(*$) some 30 years ago, very cute car, awful design on the gearbox. There is an adjustment for the 2nd gear, its on the yoke that actuates it. By loosening a bolt you can thread it in a little & try it again. DO NOT get it too tight, it will put undue stresses on the pins that hold the high speed clutch discs. Those pins are tubular, and only pressed into the rear of the low drum casting, with absolutely no support on their outer end. AWFUL! Reverse as I recall had a band adjustment but I don't remember where it was located, probably on the outside of the housing with a lock nut.
On the one I did, all those hollow pins were all bent & cracked, I replaced them with solid ones, still not great. The aluminum casting between the trans & rear axle had cracked & allowed movement, ruining the ring & pinion gear. Had to make a new casting and new gears. Anything that could have worn was so bad that many of the other internal components had to be re-made, it was a multi year project, but finally got it all done and ready to install in the car. The sad part was the owner passed on a decade or so later without ever installing it, or finishing the project.
Good Luck
Jeff