Sing along with this recording on Youtube: https://youtu.be/HspjGwjY2N8
(Click on the link and it will take you to the recording).
In bars 47 & 48, sing the melody with the sopranos rather than a continuous line of top Fs! It's incredibly high and a strain to sing otherwise. Also, on the penultimate chord of the whole piece, sing another Db rather than top Gb! Unless you really want to sing top Gb....but I'm singing Db.