Too small, the tubing needs to be bigger OD. Hope it's chromoly. The point was, you don't run the tubing parallel to the fender mount bars, you drop down (and swing in as well to compound multiple angles) to triangulate, any support added does not parallel any of that either. Different angle provides much more strength.
Yours of course and not trying to tell you what to do but you take risk once you do this on your own. We knew a guy who did his own and substandard materials and application to make a roll cage chassied car that didn't look bad at all but a combination of multiple errors there and it began when an engine exploded, the pieces fired sideways to cut the brake and fuel lines (inboard and illegal install there) and took out parts of chassis he welded up. WAY too easy. The car then caught fire at over 100 mph and flames entered the cabin through holes punched in firewall, he ended up bailing physically out of the car at around estimated 70-80 mph and clothes on fire. Probably good thing too, the car literally came apart at his welding when it then impacted concrete guardrail after he bailed. Thin wall steel that bent and cracked easily.
We had worked on it a time or two at the shop, he got the third degree about the lacking throttle return he had on tunnel ram, he swore he'd fix it. Later (before the above) he was involved in a wreck when he did a burnout where he stored car at storage facility and the throttles both stuck WFO. He lost it, car peeled through three storage buildings all unoccupied luckily and then finally plowed into a concrete retaining wall, the next thing was out on open freeway crossing at ninety degree angle. Lucky not killed then either. He survived both but smartly quit drag racing.
Not saying you at all, but once you cross the line to where YOU become the engineer, just like him you must look at EVERYTHING six times, then if it seems OK look again. Easy to forget lives can be on the line while having all the fun.
One day may tell you how we were involved in killing a guy by the same lacking of attention to details....... .............. ..not proud of it.