Pennsylvania has closed primaries, meaning you must be registered with a party to vote in their primary. Registering with a party does not mean you must vote for their candidates. Make sure your registration and party affiliation is up-to-date at https://www.pavoterservices.pa.gov/pages/voterregistrationstatus.aspx
If you live on-campus, make sure your mailing address is included in your registration. See vote.upenn.edu/register for more information.