English to Spanish to French

My native language is, as I'm certain you can assume, English.

I've learned a small bit of French and a larger bit of Spanish. Personally I am not at all interested in Spanish, but I did take three courses in high school so I know a good deal of the grammatical structure.

French I only took one course.

I only have one simple question to ask. How similar are Spanish and French grammatically? Can I apply what I know about Spanish and pick up learning French again, or should I just completely forget everything I knew and start over from a clean slate?

You have the ability to voluntarily forget things?

I'm not sure what the point of this thread is. Start learning French. Whatever Spanish grammar you know, you know. It might help or it might not help. It doesn't really matter.

Because French and Spanish are both romance (Latin derived) languages, grammar is similar.

For example:
I was parked next to the red car.
J'étais garé à côté de la [ voiture rouge ].
Estaba estacionada al lado del [carro rojo ].
The adjective (red) is placed AFTER the noun it is describing (car).

Of course the only time this isn't true is when dealing with BAGS (Beauty, Age, Goodness, & Size:  une belle femme ("a beautiful woman"))

Anyway, both French and Spanish use the gender/number rule.
Las chicas se fueron a bailar.
Chicas is feminine and plural and so "las" is used to describe chicas.
Les femmes sont très amusantes.
Femmes is feminine and plural, so "amusantes" is also.

So yes, your knowledge of Spanish grammar will help you with your French.
I know this because I am a native Spanish speaker and took French for over 2 years.