You use acetone to bond acrylic. You
Can apply it directly to the joint using a syringe works well as it tends to evaporate.
If you want you can also put acetone and some small acrylic shavings or peices in a jar and let the acrylic disolve into it thats basically all that acrylic glue is. Takes awhile to dry tho you will want to let it sit for a day to set.
As for the square you can buy them super cheap at any harware store then buy some clamps and ur all good. Nice part about using straight acetone is it will wick into the joint like soldering so you could get your peices setup and square then add the acetone.