How to avoid france residence permit?

i am an american citizen, and i am volunteering for 7 months here in france. i have now been here for 4 months. i have my long term visa but i just found out that i need a residence permit and i cannot afford it. i am trying to avoid paying the residence permit by taking a weekend to Switzerland. will this fix my problem? what do i dod? how to i avoid paying the residence permit?