Two points:

1. USE PLACEHOLDERS. Do not EVER do anything like VALUES('$seqname','$sequence','$len','$amino_acid_number','$riskeval'). Instead, do VALUES(?,?,?,?,?), and pass in $seqname, $sequence, $len, $amino_acid_number, $riskeval as extra parameters. (You'll be able to go from here to faster things later, but one step at a time...)
2. Most DBD drivers don't allow multiple statements. Try calling do three times: one for your create db, one for your drop table, and a third for your create table.

Hope that helps