go - software panics for concurrent access despite being handled by mutexes - dictionary

Question

i have a map that is being read and written by 3 goroutines constantly, the program always ends up with a "fatal error: concurrent map iteration and map write" despite me setting up the mutex to protect it, I know I could use sync.Map or I could sync with a channel but I'd really like to understand what I am doing wrong. this is the code:
//book.go
type OrderbookMap map[float64]float64
type Orderbook struct {
Bids OrderbookMap
Asks OrderbookMap
Symbol string
IsInit bool
UpdateId int
mu sync.Mutex
}
func (book *Orderbook) Init() {
book.mu.Lock()
defer book.mu.Unlock()
if book.IsInit {
return
}
book.Asks = make(OrderbookMap)
book.Bids = make(OrderbookMap)
book.IsInit = true
}
//functions with mutexes
func DelBid2(b *Orderbook, price float64) {
b.mu.Lock()
defer b.mu.Unlock()
if _, ok := b.Bids[price]; ok {
delete(b.Bids, price)
} else {
fmt.Printf("VALUE NOT FOUND %v\n", price)
}
}
func AddBid2(b *Orderbook, price float64, qty float64) {
b.mu.Lock()
defer b.mu.Unlock()
b.Bids[price] = qty
}
func GetBids2(b *Orderbook) OrderbookMap {
b.mu.Lock()
defer b.mu.Unlock()
return b.Bids
}
//TesterFile.go
func TestBookRace(t *testing.T) {
var B Orderbook
B.Init()
//add
go func() {
for {
b, q := rFloat(), rFloat()
AddBid2(&B, b, q)
fmt.Printf("ADD %v NEW: %v\n", b, GetBids2(&B))
}
}()
//del
go func() {
for {
b := rFloat()
DelBid2(&B, b)
fmt.Printf("DEL %v NEW: %v\n", b, GetBids2(&B))
}
}()
//read
go func() {
for {
fmt.Printf("READ %v\n", GetBids2(&B))
}
}()
for { time.Sleep(10 * time.Second)}
}