Spotting with mild cramps about ten days after an emergency pill is a known side effect, since it can shift your cycle and cause breakthrough bleeding before your period properly resets. It doesn't rule out pregnancy on its own though, especially with the condom slipping first.
Next Steps
Take a home urine
pregnancy test now, ideally with first morning urine, since that's the only way to be sure. If it comes back positive, or the bleeding continues, a scan can rule out an ectopic pregnancy or an early miscarriage.
Health Tips
Go in for an in-person check straightaway if the bleeding soaks more than a pad an hour, or you feel dizzy or pain on one side; please see a gynaecologist the same day if that happens.