Excel is a bad data source (no structure).
Proc import is a guessing procedure, it guesses what your data should be.
Combine the above and you will get garbage 80% of the time.
The best suggestion, as always, is to convert your data to a better format plain text (i.e. open, cross platform) such as CSV (which Excel can save to), XML, Json. Then with that nice datasource, write a datastep import program which reads the plain text file using formats, lengths, informats, which you - the person who knows the data best (with your data import agreement) - supplies so the data is read correctly and repeatable each time.
I suspect however that none of the above is what will happen, so you can either fix it after proc import, try to force it by adding a row into Excel, or some other bad trick to get round the situation without fixing it. But you will find many many topics on here about this very thing and its due to Excel+Proc Import = bad.