The amount you cut is minor and the fit is full width of the Steppie Bed.
Sealing it is the thing, you need a good “2-Part Epoxy”, mix it up according to instructions and put some in, tape the end and stand it on the end with the tape, let it dry.
Do the same for the other end once the Epoxy is dry.
Make sure the light strip fits before plugging the ends and be careful of the wirings and PCB when cutting.
This WILL work, you just need to be careful.