*Is this a proper sentence?

[Unregistered]

I can't wait to try on these cool pants that I got lucky finding at the store.

[Raymott]

I can't wait to try on these cool pants that I got lucky finding at the store.

Yes, it sounds correct to me.
This is the diploma that I succeeded in achieving at university last year.
The "in" in "got lucky in finding" is understood in your sentence.