Friendship worries

So i 18 (F) have just moved to university this year and have made a friend on my course who i have agreed to live with next year. We have clicked quite well and gone out a few times. Problem is she 18 (F) is really inconsistent when answering the phone. Sometimes she responds right away and other times it takes days for her to respond but this time she has read my message but hasn’t replied and it has been a day. Is this a hint that she doesn’t want to be my friend? I have a few issues with rejection and can be a little insecure sometimes so am i just overthinking this?