You begin planning

You wake up with Mrs Figg by your side, she transformed to almost everybody in the community including that chick from the metro. It looks like Mrs Figg has a greater outreach than you have expected. You collaborated with her in milking production and in addition to the lust potion drops, your cum was added in every supply.

This way you were able to walk on the streets and the muggles(including men) in the vicinity are aiding to your cause. Even barely legal teens would flash at you and would request for a cumshot.

Mrs Figg didn't like keeping to one appearance a day(or an hour at times) and hence would change whenever needed.

Now the reason why Aunt Petunia was not under your control even though they drink from the same milk supply was the protection spell cast by you at Hogwarts when fighting against Voldemort. It backfired as now, you are considered a threat hence it is disabled. However, Marge is not under the spell hence you need to corrupt her before reaching Petunia.

You note down Marge's schedule on arriving here. She was smart enough to not drink the supply hence it became more and more difficult. But there was a way in.