This is not meant to sound as harsh as it might but I think you need to get your mix right before you consider mastering. Mastering is something that is done for finalising something to fit the medium and intended context it is not mandatory.
A quick analysis in Youlean shows me a red line across the top which means it is in a permanent state of clipping and the strings in the background, I assume they are strings, sound more like square waves than strings
Most Streaming sites would not allow something with -5.4 LUFS you have,they lie around the -14LUFS.
As noted above LANDR hum questionable.
The last thing I would ask is why do you think your tracks needs mastering?