Cpatrikis

hey everyone, i'm new to this site but had some concerns about my new plant!
i just got a musa basjoo last week in the mail. when it arrived it had 2 leaves on it, one had been clipped (i guess to help it fit in the box) and one was looking beautiful. the third however had brown all along the edges and appeared to be drying out. i decieded to try and trim off some of the brown but after a few days the brown just kept spreading. only about half of that leaf is still green and it is slightly yellow with brown spots. should i just clip this leaf completly?
also a new leaf was shooting up the past few days and was growing about half an inch a day. it is about 7 and a half inches now and is almost completely open. i watered the plant last night and when i woke up i noticed a few small brown spots on the original healthy leaf and 2 small brown spots on the edges of the new leaf.
i think it might be because i watered it too much and did not let the soil dry a full 3 inches down. (i am using a soil of all organic earthworm castings and sand for air and water)

Any suggestions? please help!

also you can see some of the spots on the larger leaf on my main profile picture if you look at it.

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Chris